Hmm.

I rarely wear a cross. Only when I'm going somewhere, for example, and there's a chance I'll be visiting a church (like when I went to Karelia, to Valaam). I didn't take it off then, and it was incredibly annoying, just awful, but there was nowhere to put it, and I was afraid of losing it.
By the way, once I visited my grandmother, took it off, and misplaced it. A day before I was leaving, I realized it was gone, and we turned the whole house upside down, but we couldn't find it. I was upset, went to bed, and dreamed about where to look for it. In the morning, I woke up, looked, and there it was, lying right there. The funniest thing is, I had already looked there before and turned everything upside down, but didn't find it, and then it was lying almost in plain sight.
But I almost never take off my earrings. I have two pairs of gold earrings; I took one pair from my mom, they're small leaves with a small pendant, and the other pair is mine, fancy gold rings. I wear those for months, only occasionally switching them out, and sometimes I wear other ones just to show off.
But if we're talking about a pendant, I'd suggest something simple, maybe with the symbolism of your favorite anime/game, or something that looks like a military dog tag, you know, whatever you like.