One of my favorite ways to customize sutff is by using bleach to (literaly) paint designs on fabric. It's so versatile and fun! More durable than paint if you don't have special fabric paint and only acrylics. You can do it on pretty much all fabrics; just make sure to wash before using/wearing what you custommed!
I'll drop some pics of the Bauhaus shirt I made. (guess my favorite song from them, I suppose.)
Pretty sure it's a well-known DIY. But anyway, thought I'd share it.
Have you tried it before? If not, will you?
Have fun.