A couple of things that I can recommend from experience...
If the doctor hasn't recommended a meter, I'd get an UltraMini from OneTouch
http://www.onetouchdiabetes.com/ultraminior another really small one that can travel and uses the same type of strips that the meter from the doctor recommends. I use this one to travel with rather than the larger one, and it can fit into short pockets with a few lancets and miscellaneous stuff in a baggie easy. That way he can test his sugars when he's feeling wonky.
Plan mini-meals instead of larger meals during the day, especially when you're touring the parks (hubby calls this the Hobbit eating plan). The portions at the quick service places at Disney are huge, so what my hubby and I have gotten in the habit of splitting one of the combos when we get hungry. We eat breakfast in our room, get a combo about 11-ish, another about 3-ish, then dinner. So we have breakfast, second breakfast, 11-ies, lunch, high tea.... If you're on the dining plan and get QS combos, look for the places that allow a piece of fruit for dessert instead of the pre-packaged desserts- you can carry it around for later.
Especially if he's on meds for the first time, pay attention to what he looks like and what's he "normal" and what's his "off". New meds in combination with increase in exercise will drop blood sugars like crazy, and if he's new to diabetes (and a lot of times even if you're not) when your levels drop rapidly you have a hard time telling or explaining...
Also, make sure to make allowances for adrenaline. I have a hard time telling until it's way too late when my sugars are dropping, especially with all the excitement of Disney, so my hubby has learned some of my physical tells, and we carry some hard candy or other things that doesn't melt in the heat that will raise blood sugars relatively quickly. Sometimes the lines are just too long for a coke or an ice cream or a piece of fruit to pick up the sugars.