I haven't thought of this much....
I don't wear certain clothes to piano lessons or for practising, I just wear what I'm wearing that day.

Right now I always wear long sleeves though, because it's winter here and its cold!!! My hands get cold really easy. Depending on my mood, I'll roll up my sleeves. Sometimes long sleeves bother me, other times I don't even notice them.
And I can never wear bracelets when playing. I love bracelets though, so I always have to take them off before I play. I used to wear a watch, but I lost it...
I don't wear shoes around the house, so I practise barefoot!
I have a recorder with me too when I practise! And a pencil, and eraser.
The uncomfortable clothes issue only comes up during recitals... I choose dresses that a comfy, and I wear flats. I find it hard to pedal in running shoes, heels, or anything with a thick sole. My foot needs to be able to feel the pedal.