Wondering if anyone else had this issue. In Egypt, I got the Servant's Quarters key and used it to finish that group of adventures. The key is still in my inventory, however. I don't know if I should get rid of it or if there is another place to use it.

i havent dont the servants quarters yet but i think theres another part to the adventure, i suggest holding on to it just in case.

After returning from vacation my sims seem to have a variety of keystones in their inventories even though they have fully completed the tombs. I just leave them there in case I need them in future, but I never have.

Yeah, I still had the "Ancient Monk" key after finishing that tomb, I just kept it to be "safe", but never had to use it again ...

You can buy a treasure chest from the special merchant in Egypt and use it to store your keystones until you are about to go on an adventure. I keep the chest by the TV, grab my keystones, my tent and other necessities and take down my Panchu's Axe from the wall. Then I hit the "Travel" option and I'm good to go.