I've had migranes since I was 7 years old. I'm 31 now. I've taken Inderal every day of my life since I was 7. I have Anaprox (sp) for when they are coming on slightly and have done/do the Immitrex/Maxalt/Relpax meds when they are bad or I know they will be. I am married to my DH today because of the care and attention he gave to me (early in our relationship) when we went to Cedar Point Amusement Park and I got a migrane. (To put up with me under such circumstances and not complain, I knew he was a keeper). So while good can come from crappy situations, I try to avoid them because I know how brutal a migrane can be and how it can ruin a trip. Here's what I've learned:
1) I ALWAYS remember my meds. I was shut in a hotel room for 1 1/2 days with no lights on, no TV, no sounds at all because I couldn't move and didn't have my meds...Never Again. (Only a trip to the ER resolved this migrane). Now I remember my meds and I take them as soon as I feel one coming on. We stop what we are doing (inconvenient yes but not as inconvenient as 1 - 2 days in a dark hotel room) and I return for a nap to let the meds kick in.
2) I stay away from rides that jerk my head. I LOVE roller coasters, the bigger the better and upside down is fine, but not anything that will jerk my head from side to side and bang it.
3) Stay hydrated as you said.
4) Take the time to eat something while in air conditioning. Lack of food triggers a migrane for me. I don't like to eat a lot when its hot and humid, but I try to resist the urge to live on ice cream alone because I could trigger a migrane.
5) I force myself to get sleep. I pack and prep like a crazy person before we go on vacation, staying up late and I already only get 5-6 hours of sleep a night normally. I can run on adrenaline for a while, but when I crash I crash and it contributes to migranes. There is so much to do on vacation, but sleep relaxation are important to avoid migranes.
6) I wear sunglasses. I cannot be in the sun without them or I will get a migrane.
7) I try to remain calm and stress free. After all, I did my research and planning and there is nothing to stress over, its vacation.
Still I say catching the migrane when its starting and getting to the room to take meds and rest is the number one thing that works for me. If my family wants to stay and enjoy, that's fine and I'd probably prefer it because I need quiet time, but I need to get back to the hotel room quick. If I catch it quick I can usually be ok in a few (2) hours or less. If not, it takes much longer.
Good luck and know you aren't alone.