My friend Laura introduced me to this tool last weekend:
It comes in super handy! It's also nice and small, so it easily fits into your bag, and it's only $4.99 with free shipping on Ebay.
This is my absolute favorite multi-tool; i.e. 3mm, 4mm, 5mm, 6mm, and 8mm hex wrenches; 8mm, 9mm, and 10mm socket wrenches; and a straight blade screwdriver. Light weight. Portable.