I do my best but allow myself some leeway. Life is too short not to be able to enjoy the odd treat. The trick, I've found, is to decide each morning what your treat is going to be - ice cream, wine, sweets etc. - and enjoy that treat, or treats, without feeling guilty. That way, you're getting the holiday experience and not feeling deprived. If you gain a bit, so be it - you'll soon get rid of it when you get properly back on plan.
Try to plan your first day or two back before you go away as getting back on the wagon is so much easier if you're organised. Perhaps you could do an internet shop for delivery as soon as you get back?