pinz, fabric paint! (or acrylic like me xD) safety pinz, charms, studs are cool!! the tabs from cans, stickers, you can also stitch stuff like your name on it!! hope this helps luv luv <33
Lots of good tips above BUT! I would like to add some other tips here too—
I've lost some really cool pins over the years and one tip is to break off little chunks of an eraser and to put it on the actual sharp pin point after putting it thru the bags material (far enough onto it that it can still close obvs) before closing it so that if it DOES open up, it's going to be a lot harder for it to fall off your bag and get lost foreverrr