It's just as easy to donate something back as it is to trash it.
As so many people have already posted, lots of the stuff getting trashed is desired by others.
I don't trash anything, and I won't sell stuff back to Gaia unless it is available in the gold stores.
I don't hate any of the items I get. I'd even keep all the cat items even if i abhor those animals irl. Some of those 'trash' can be useful too (e.g., as alchemy ingredients or selling them through my invo if it's possible).
I keep nearly everything. I sometimes trash the Aquarium backgrounds but I'm often online at night when the dumpster gets empty so I usually save them for when it needs items to start functioning again.
I have not really dumpster dived much but some items that annoy the ******** out of me are the neutral starter clothes. I used to get those all the time from the lottery thing years ago, and have gotten more since I started back up..sad