I just went thru the same decision last Friday 9/20/19 with our 6 year old kitty Sierra & know exactly how you are feeling right now! I always keep their collar & tag ( I do wash & let dry 1st ), a bit of their fur & a whisker ( never have had any foot prints as vets around here don't do that, wish they would! ) & put them all in a small zip-lock bag & write their names & birth date ( if we know ) or adoption date & then the date they crossed the rainbow bridge. A few times I did take before & after photos if I didn't have any or many of them ( for feral or outside kitties ). And I now have a ritual that I do as a way of dealing with my loss / grief. I rarely share this with people because if you are not a pet owner/lover you probably wouldn't understand, but it helps me a lot. The 1st time I did it the kitty in question had been thru a lot & their fur wasn't clean & I just couldn't bury them looking "unkept". So I decided to bath & blow dry them before wrapping them for burial ( I use 2 or 3 layers of wee pads to wrap/secure & then finish with a clear plastic garbage bag. I also use an index card & put their Name, birth or adoption date & date they passed & then write either something about them or to them, then enclose that in a smaller zip bag & tape that to the last layer of wee pad before wrapping in the clear bag. We have buried every cat we've owned or rescued ( & in 46 years of marriage that's been quite a few! ) so I've had to dig a lot of graves & lay them to rest over the years. But it's getting harder for me to do at my age & health, so I don't know what I'll do in the future. We don't have any pet crematories any where close & after running up a vet bill of around $2000.00 in the past 3 weeks, I just couldn't afford another $300.00 ( or more ) for cremation! Thankfully I never set-up the glucose meter or used any of those supply so Wal-Mart should issue a refund ( will find that out tomorrow ). So as everyone else has said You do what you need/want to do. This is your kitty & you know what memories you want/need to have/keep. And no matter what you don't ever let anyone ( friends or family ) poo-poo your decisions on how you need to deal with your grief. There are more of us who know what it's like & we will stand together & support each other during this time of grief!