I'm not going to pay for food and supplies for a camping trip I wasn't able to go on
Why weren't you able to go on the trip?
I just wasn't able to go. I haven't been on a camping trip since the 3rd grade!
If you can't go you shouldn't have to pay for it. They will understand if you don't.
Oh good. I am certainly not going to pay them.
No one should expect you to pay for a trip that you could not go on.