I'm not talking about inspections done by an inspector Fred Griffin Florida Real Estate but ca couple of personal instances I remember was:

1) I was showing an old home in a neighboring town a home and we were curious about the attic. I lifted up the entrance and it rained a ton of mouse (or maybe bat) crap down before I could get the cover fully back in place. Of course it covered both of us.

2) In the attic of  a 100 year old vacant home I had listed I checked the attic out and it had several family (home made) treasures in it. I told the owner about it and she asked if I would hall it to the curb for garbage collection. I asked if she was sure and she said yes, she was aware of what was up there. Several items (Christmas) went home with me and we break them out every Christmas season.

The attic inspection revealed the house had been on fire at some point in the past. 

Water stains from old and active roof leaks, vents venting into attic vs. outside, beehives discovered, racoon discovered, owl discovered (and gaping access holes or vent screens missing) and once a jar full of silver dollars discovered - I had a very honest inspector that day!

I once had a listing where during the home inspection, the inspector looked into the crawl space through a small door high on the wall. I don't remember which room it was in but it struck me as unusual.

What the inspector asked, about the house which was fairly new, was "Why an I not seeing any insulation?".

We contacted the builder. A work party was sent to the house and insulation was blown in through the open door...at the expense of the builder.

The main things we find in attic inspections are wiring and venting problems.

Good morning, Fred. I rarely see anything that is problematic in an attic on an inspection report. I did some years have one that had a bat infestation, however. Not cheap to get rid of bats.

I’ve heard of snakes skins being found, and I am not all right with that.

I've seen broken HVAC ducting, stains from past water leaks, debris from prior owners, rat poop, older work not up to modern codes.  Nothing too crazy.

With that said, we do buy houses that people want to offload and we've had homes FULL of belongings, including attics.  Everything from costume jewelry, to Marine Corps Dress Blues, to garages full of older power tools and hand tools, and of course lots of books, clothing, photos, and loose coins.  I found between $10 to $20 in coins in quite a few homes.  In two weeks we close on another house like that and, as Texas Mary from Storage Wars would say, there are some "Treasures" there too!

I think we're up to three pianos we've had to have hauled to the dump because NO ONE wanted them.  I've given many a piece of antique furniture away to friends to restore.  The library at one point banned me from donating books we were bringing so many over from one house (over 100 books... and that's not counting the ones we kept).  Many a church group/homeless shelter/etc. has benefited from left-behind clothing.

And for the Marine Blues, those went to the local Army/Navy Surplus Store with strict instructions that they go to a Marine in financial need.  Owner is a Retired Marine, he saw to it personally.

recently we had one with critters.  But all insulation was changed, feces removed, traps set, repairs made to entrance site and all was well.

Good question to explore thank you Fred Griffin Florida Real Estate ...Fred, attics as we know is where heat of the house rises & stores itself. Venting is so important as is turbines, insulation, & even putting foil insulation between the rafters that reduces heat & also cools by 5% or more. Access is dicey as most older homes were never built to do work in the attic spaces. Today, we look at it differently with newer homes. I have been in attics where you can walk around vs crawl around. Note that insects, vermin & other life-forms actually nest in the attic heat & take refuge in the walls to cool off. I personally installed double the size vents (2), a wind turbine & insulation between rafters in my old home to dissuade heat & allow A/C to function with less efforts. On work done in literal "crawl" spaces, college kids will do anything for a buck! LOL. P.S. people store valuables in attics so in estate or probate sales, check the attic for "goodies". One guy had a decent coin collection

PIGEONS. You have not lived until you have seen the handy dandy guy take out five bags of dead pigeons from the attic in a rental home after they vacated.

One again, Fred Griffin Florida Real Estate my response is:

All of the Above. 

Nothing that was a show stopper, ask "deal breaker". 

Working with  buyer, had  a home inspection reveal there had been a fire in the attic a few years back.  my buyes decided to move on.

Upon inspection a home where the property disclosure stated "no radon", a disconnected radon mitigation device was discovered under heavy insulation  in the attic. DEAL BLOWN? Nope - as the broker offer to pay for a "radon test" to see what was going on. NO RADON! Why? Radon had moved on and no remediation was necessary. The owner was unaware of a radon issue when he purchased. Buyer said "let's close"!

Moral of the story: For your protection get a home inspection and maybe a reason test!

Great reading material here.  I am sorry to respond that I can't compete.  

Besides squirrels, stink bugs, an adult filming studio, and mold...nothing to report

All of the above! I have one now that has an LVL that was improperly installed and remedying that could be a bear. 

All of the above, Fred, you named it! What we have to be mindful of is illegal use of attics, e.g. sellers calling them living space (even if fully set up as such, maybe as a work or nanny area), which is not legal since there is no safe egress in case of fire (at least in most cases). 

I remember showing up to meet buyers for the inspection summary and seeing the inspector getting out of the attic on a hot summer day.  It was certainly over 100 degrees, and it turned out that the HVAC was not working either.  He definitely always went above and beyond for my clients and it was greatly appreciated.

Oh man probably one of the worst attics was when the inspector found that MANY of the trusses were cut and causing severe  damage to  the weight load. Of course our buyers walked away.  Good grief!

Mostly inadequate ventilation where mold grows on the underside of the roof decking. Easy enough to fix but buyers get really upset.

I did witness a muscular raccoon rip off the attic fan on the roof when I was in the driveway of my short sale.  I think he did it just to show me he could!

In Colorado, we have basements for storage, so don't see much "stuff" in the attic.  BUT, remember one inspection in Bennett (rural and on acreage) that had skunks multiplying in the window wells and raccoons in the attic.   I remember the seller having a difficult time eliminating all the feces in the attic and sealing it so they didn't get in again.

Hello I seem to recall one time seeing a raccoon in the attic doing the inspection and he was eating the wiring up there.

There are better ways to inspect roof and insulation. When one sees pin holes above you, dead rats and walnut shells under the insulation you know you got a big problem. Most inspectors are too heavy to walk on it. As for my house I have put walking planks around such an inspector will not talk on the ceiling boards make a dent.