2 - 8mm/10mm wrenches (one open end and one box, both ignition wrench sized)
1" stub of an 8mm allen wrench (used with 8mm box end)
Swiss army knife
Multi-tool (a very basic one)
Chain rivet tool
Cassette removal tool (Unior)
Tire pressure gauge
If you need to pack or unpack the bike for the plane or train a pedal wrench is needed. A 15mm cone wrench will suffice if the pedals are not super tight. The Park Bicycle Tool RW-3 Headset Pedal Wrench Combo is another option. It is a short stubby wrench.