What can I do?

I would guess that you could take him back to court over this or forbid your son to go but it seems like both are situations that are a no-win for you. In reading all of this it seems like your ex’s motivation is to hurt you and get to you emotionally and financially. As long as he is paying for things just blow it off and act unconcerned. After all, this probably is a good opportunity for your son, just unfortunate that it isn’t discussed w/ you ahead of time. If you don’t react at all or react positively won’t this bug your ex? Maybe he will stop this?
Could you talk to your son and explain how things are supposed to work? He must be old enough now to understand this.

Custody…50/50…joint legal…one week with me, one week with ex as specified in Court Order. Time and time again ex signs my son up for trips, camps, etc. that takes away my time. The judge in my case refuses to recognize my custodial time although I have brought contempt charges against my ex. Judge states I have “no evidence” and does absolutely nothing. Therefore, I feel I have no rights whatsoever and that it is futile for me to even try to bring anything to the Court’s attention. It has now happened again. Ex has signed my son up for travel for three weeks out of the country this summer. This takes away two weeks of my time without my consent or agreement. In the past, I have been forced to pay 50% of the cost as well as relinquish my time when I had nothing to do with any of this! The Order regarding expenses has now been changed. Ex is responsible for his extracurricular expenses and I am responsible for mine. I cannot afford the things that he can and the judge refused to make my ex pay me for expenses when the 50% order was in place, but I have to pay the ex for 50% of his extravagant expenses. I was given over a year to pay these expenses which were sizable. Has anyone ever heard of anything like this? What on earth am I supposed to do?