I just spent a week out of town, and managed to lose a couple pounds in the process!
All it took was being conscious of the food choices I was making, and logging what I could, and guessing at the rest using MFPs food data base to get some kind of idea about where my calories sat for the day. Over the last 5 weeks I've had several graduation parties, my husband's included, as well as graduation day itself and all the snacking involved with that, my anniversary, and my husband's birthday and their various celebratory food events, and other social obligations. (I picked a heck of a time to come back, right?) And I still managed to lose weight for the month, just by being conscious and aware of portions and food choices. There have been days that I just said "eff it!" and ate the bad foods and the cakes and stuff, then got right back to it. I've still managed to see a loss each week.
A few years ago, I had lost several pounds (over 30) before I got married, went away on my honeymoon and gained 7 pounds, then just got right back to it, and had no problems. I just told myself to enjoy my honeymoon, and as soon as I was at home, it's back to eating properly.
I think that's why I do okay, actually... I only go "off plan" if I'm not in my home. Eating out with family and friends and such, I will fall off, but as soon as I'm home again, I know I'm back at it. Probably because of the absence of junk food and the food scale sitting on the counter.
I hope you have fun with your friend, and don't let your weight loss get in the way of making memories and having a great time! Put something up on your refrigerator door to remind you when you're done with your vacation time to get back to business.