You need to take the equipment with you. A few days without expressing will not really affect your supply and your little guy is more than capable of building it up again afterwards. But being engorged and having blocked ducts is no fun at the best of times, and juggling around on a horse with engorged boobs sounds like hell.
So take the hand pump, and if you feel full express until you are comfy. Feel free to chuck it out. Even hand-squirting into a big towel can get rid of the excess milk and make you more comfy - or hand-expressing down the sink in a public loo.