If you are thinking of necessities, there are several mentioned already. If you are thinking of memories I can think of items from planets or stations that have little value or meaning to others like;
The formidable coffee cup from XYZ.
Inside the cup
A broken trophy, ring or jewelry piece from an event or relationship.
A rock or a smooth colored stone from a walk or romantic encounter.
A ball/toy from mom, dad, bro, sis, even favorite pet.
A picture of the guys or girls in a bar from some outlandish place with an unmentionable tale from where the night ended.
Door or bunk plate with name on it.
Coins, credits, whatever from various markets, cities and planets visited.
The broken knob off some device that either almost got you killed or saved your life.
The key to I don't know where and what lock.
There's what I can think of as points of reflection versus like I said necessity.