What would you do?

I'm a teacher (pumping on my prep right now )  and I need some advice. We take our students on an overnight field trip to our state capital. Originally DH was going to come along as an extra chaperone and bring DS with him. However, it turns out DH has to work and I don't really want him to take two days off and lose two days of pay to go. Although I am dreading being away from DS, I'm trying to figure out what to do in terms of pumping (I EP). I will probably end up having to pump on the school bus once the kids are off when we make stops at least twice each day we are gone. Would you bring a cooler and fill it with ice in hopes of saving your milk (we leave at like 6am-- I will pump before I leave home and we don't arrive to where we are spending the night where they will have a fridge/freezer until about 6pm)? Or would you pump and dump? I really don't want to dump it but I'm also paranoid that it won't last either... any thoughts would be appreciated!