You can take medication with you, but it's hard to tell for sure how you will be till you have started. I was absolutely fine, and could easily have gone on holiday. If your chemo is three weekly, then you will be mid cycle and less likely to feel unwell. You'll be disappointed if you cancel and then find you didn't need to and if you are not at your all time brightest, a holiday will do you good. With your oncologist's OK, it's worth the relatively small risk! Have a good time.