Ideas from AbsorbingSafe11 & TerminalSnark:

• top hat like the lucky hat
• Coloring: black hat with a (changeable) colored ribbon
• Effects:

you could play up the stage magic connection by making it portable storage accessed with a keybind, like a backpack that you wear on your head.
Or you could make it usable to spawn a rabbit with a relatively minor cooldown. Or pull out a random item like a random flower, a damaged iron sword, a rabbit haunch, maybe a small bundle of carpet instead of a string of silk scarves.

Open questions: single time usage? Durability? Avoid endless items...
Maybe a wand for the magic?