Mega-Watch is a really good one! But I'd personally go for a Mega-Pocketwatch, because it would be fancy af. It's also a nice reference to previous generation RNG manipulation ^^
Mega-Sword also sounds really awesome to me, but it would not really fit me because I'm not very violent anymore, and prefer long range attacks where you don't have to be near the opposition or contact them directly in any way. So a Mega-Bow for me would be more fitting if it were a weapon, or a 'Mega-Wand' of sorts (referring to my IRL name, because my parents were crazy), perhaps even a gun. Probably a wand though, because however awesome the other weapons are, and however alluring it would be to scream 'Mega-Uchigatana!' and fantasize myself as a really noble warrior, that's all it would ever be, a fantasy. Not that a wand would not be fantasy, but the fact alone that I'm so focused on fantasies and ideas and stuff like that indicate that I would probably wield some magical weapon associated with mentally orientated warriors or wizards.
Though Pocketwatch is still a great contender as well. IRL I have the habit of writing down times, to the second (and even noting timezones and offsets), whenever I want to remember something. I do it less now than I used to, but it's really typical, and I find a lot of support in 'time' in general. I know time is relative, but to me the definition of time is 'change', and in that sense it fits me a lot (and also fits Mega-Evolution a lot!). I just wouldn't be a character that battles a lot, I wouldn't be a warrior. But that's no big deal to me. In life I'm more of a wanderer as well, though I battle fiercely for the things I personally believe in.
Sorry for stealing and adjusting the other ideas in this thread though! I just really appreciate them I guess, and they have inspired me.