If you're looking for a nice compact seat bag, get Specialized's Mini-Wedgie. It's large enough to carry the essentials like a tube, patch kit, tire levers and a mini tool, while its water-resistant coating and zipper keep your gear dry. It even has an internal neoprene tool pocket for easy access and to protect your spare tube from getting punctured. What's more, the Mini-Wedgie attaches in a snap and stays put thanks to its handy hook-and-loop straps.