What muscles need to be strengthened for a 5 day backpacking trip?

I only weigh 105 and was told I won’t be able to carry much on my backpacking trip, but I don’t want to be a burden to my crew. So in the spirit of wanting to pull my own weight, what muscles should I strengthen?

We will be backpacking 4 and 1/2 days in the Pecos Wilderness of New Mexico.