I carry a mini multi tool in all my seat bags. My favorite is the SOG Crossgrip (2.0 oz/57g) which is no longer available. I also have a Gerber Clutch (2.6oz73g). Both are much lighter than a full size Leatherman which runs around 8.5 oz. They come in handy especially when I need some pliers - had to use it to pull a piece of wire out of a tire not long ago. A also carry a Topeak Mini 15 tool set (1.55oz/45g w/o case - unfortunately no longer available as well). With the SOG and Mini 15 I can make most repairs short of removing a cassette. I also carry the chain tool for the Mini 15.
mike