For take-along tools on a bike all you really need are tubes, a set of tile levers, and a a few metric Allen wrenches (4,5 and 6 mm and perhaps 3mm) which can be had very inexpensively even for good quality ones. A small screwdriver and, for a few older bikes, 8, 9 and 10mm box end wrenches may be needed.

Park Tools sells the MT-1 "Dog Bone" multi-tool with 3,4,5,6 and 8 mm Allen bits, 8,9,1nd 10 mm boxes and a small flat screwdriver blade all in a flat, thin, one piece 50 gm tool for about $10. The allen keys are positioned so the larger ones have good leverage. Get one of these and dedicate it to your bike and you need almost nothing else.