I would want...Uh. Huh. Um... I have no idea. Maybe...no, that's stupid. What about...? Wait, no, I could just buy that. Those actually exist....[small]poptarts[/small]? I really have no idea. There's just too much awesome. I can't choose.
I guess I could name all of the things that I was talking about, before. That might help me come up with something.
In order:
Akaviri Katana
Glock 20
Ghillie Suit
Yeah, still nothing. Unless I want to buy a ghillie suit, and wish for an M40A3 with an assault scope to go with it.
T51-b powered armour? Nah, impractical.
I seriously have no idea. What about some sort of crystal that emits water? End the world's water crisis before it even picks up with that, eventually. And right now, I'd be able to fill up my water cooler without having to get up and lug it over to the sink, put it in the sink, take off the top, put a funnel in the top, and wait for ten minutes while the painfully slow filtered water tap fills it...
If we're allowed to choose people, I might pick my child character Cassandra from Fallout 3. I've always wanted a little sister. Just too bad that the only sibling I have is a big brother. (Niko voice) Who is also...kind of a dick.
If I'm allowed to choose cheats as long as they're useless, I might choose infinite Fallout 3 bottle caps. That wouldn't be so useless, though, since I'm the meanest genius! I could sell them to collectors. Both those who would want to collect a 1:1 scale, full replica of a Fallout 3 bottle cap, and those that collect bottle caps period. And since they're (Presumably!) made out of solid steel, they could be melted down. No shortage of metal!
But any one of those three. Equal enjoyment. One is fresh water, and eventually averting crisis. One is a person I can even closer than my best mate to. I was always pretty close to my parents, but we (My parents and me) are very different. I'd probably be able to get very close to a sister my age. A best mate is great and all, but nothing beats the bond between kin. And one is a good source of money, and scrap metal will always be on hand.
Hard to choose. Maybe you, the OP, could choose one. Based on parameters, or based on what you think is best.