Your mixer is the sulfite culprit in that drink. It's full of sugars, probably corn syrup and other corn sugars. If you have true sulfite "allergy," not the more common "sensitivity," You could react to only 1 drink.
Are you sure you have a sulfite allergy? Have you seen an allergist, done food challenge testing, keeping a journal? Have you tried the mixer without the vodka? I actually wouldn't try drinking the mixer or any other food testing except under a doctor's supervision. Getting hives is a serious reaction. Your doctor might want you to have an epi pen on hand, maybe 2 of them, as 1 only lasts briefly.
Meantime, do you really have to drink to have fun and relax on your holiday? Even some brands of mineral water are sulfited (see google), so maybe stick to fresh squeezed orange juice. Stay far away from any drink, soft or otherwise, that has lemon juice unless you see the fresh lemon. Bottled lemon juice is very high in sulfite. Frozen lemon juice is clean. While you're avoiding drinks, I'd also research foods you might try where you are going.
There is a book available that lists sulfite content of specific brands of foods, drinks, medicines, etc. It's not free, but it's the only resource I know of with this research. http://www.learningtarget.com/nosulfites/index.htm
. I have no affiliation with the author, but I did get the book after reading the free online book over and over and learning a lot. My reaction to too much sulfite is life-threatening, and I have made good use of the tables in the book to avoid reactions.