i often have this problem. the wrislet would be perfect to take along. i don't want to carry a purse, but stuffing your cell phone in your pocket feels weird and it really bulges out, it's not like you can't tell.
if it's a concert, i wouldn't wear something designer. i'd just be afraid it'd get ruined. i agree, just wear something cute and not sloppy looking like a band tee shirt. (when my friends and i were teens we used to just wear the band tee shirts to concerts and roll them up, although i wouldn't advise that, but heyy we were a little younger than we are now so we didn't know better, right?)