I'm not going to drive over to my friends house while he's on break from school because I already have plans.
Do you want to try and go with me on this?
Let's go ahead and make sure we can get to meet up.
It's understandable to not want to cancel your plans just because a friend has free time. However, if your friend is on break and you rarely get to see them it may be worth canceling other plans. If you can't change your plans around to accommodate a friend he rarely see, then the relationship is bound to fall apart.
Why should I care about the relationship with my friend if I have things to do?
Well this could hurt your friends feelings as they can see that they are not a priority to you. If you want to use your time elsewhere that is fine, but you can be honest with your friend about it.