I have a Topeak MTX DXP trunk bag/pannier set, so I've got lots of room. In that, I keep an entire clip-on saddle bag that includes a tire lever, tire patches, Presta to Schrader converter (I fix other people's tires more often than I fix my own), stand-alone chain tool, small length of spare chain, individual Allen wrenches, small screwdriver, individual flat wrenches, spoke repair kit, tire boot, 2 Band-Aids, rubber gloves, identification/medical info card, a quarter, and a $5 bill. When I don't need to carry the whole trunk bag, I can just slide it off the rack and clip the saddle bag under my saddle so I have any necessary tools to handle a breakdown.

Alongside the saddle bag in the trunk bag's main compartment, I keep a pencil case filled with miscellaneous first-aid items, a second spare tube (the first is rolled in a sock and strapped to the top of my rear rack), my mp3 player and speaker (when foul weather requires me to remove them from the handlebars), spare batteries, lunch, and miscellaneous clothing and other items I need for work.

Wish I had a photo, but I am too lazy to go out to the garage and take one right now.