Just about anything I insert in there feels either good or painfully good.
As for what's gone in there and beyond; a 12" double ended dildo and a 17" double ended dildo. Both of theses entered past my rectumn and deep into my colon. Despite being somewhat panic-stricken, they still felt great!
As for things that have been inserted all the way in a controlled manner; a 12" double ended dildo (a different one to the one that went in too deep), a 6" regular dildo with a flimsy flared base, a 36" colon snake (pushed in further with the 12" double ender), 3 golf balls, about 6 mandarins (the first one I inserted went in too far after being pushed in further by the others), 3 lemons, 3 hard boiled eggs (shells removed), bar of soap. Not much more that I can remember.
As for how long I've kept them in the for, apart from the 2 that went in too deep, no longer than about 30 minutes. I'd get the urge to go, so I'd give in.
Thankfully, no ER visits. By "controlled" I mean not cuming, that's how the other 2 double ender's made their way in too deep.