Ds is two and we traveled during early December so the heat wasn't an issue for us.
1. With dd (now 6.5yo) we traveled w/ the backpack diaper bag...which on a long day was worth carrying.. but w/ ds I just tossed some diapers and travel wipes in my Baggalini and the changing pad from the diaper bag in the bottom of the stroller. SOOOO much easier!
2. Bring small beloved toys to play with while in lines. Ds loves Thomas. He had at least one train in each hand and sometimes a third! He was quite content playing w/ his choo choos while waiting!
3. We brought disposable sippy cups w/ us (First Years has Disney themed ones). Didn't have to worry if we left it somewhere! We only used them on the go, the restaurant drinks were fine for him w/ the straw.
4. Plan out your time with space to be flexible. We started out w/ our first three days as 1/2 days in the park (1/2 MK on arrival, 1/2 Epcot on day 2 and 1/2 Animal Kingdom on day 3). This allowed us to relax and take it easy. Over days 4-9 we closed the parks two times, but had sleep in days the following day. With this schedule we didn't have to go back to the resort for a nap (and on the long days, ds just collapsed in the stroller or the carrier).
5. Character Meals - Ds LOVED them! He was all smiles at whichever one we went to...even the princesses!
6. I packed our suitcases w/ both kid's clothes separated by outfit in 1 gallong zip locs...including everything (socks, etc). Dd's had underwear and socks, ds' only had socks. MUCH easier than pawing through all their clothes looking for matching stuff! All I had to do is pull out the bag and toss it on the table to get ready for the next day!
7. We used a Beco carrier for ds (30lbs at the time) when he was tired. We didn't use it when he was awake as he much prefers to be mobile, but when he was tired and needed to sleep it was priceless. Dh carried him as much as I did and when ds was in the carrier...dd jumped in the stroller!
8. Monkey Backpack w/ Leash - Every kid is different. We never even thought about using a leash w/ dd at WDW back when she was a toddler. She was perfectly happy to hold our hands...heck we didn't even have a carrier for her then. Ds is a totally different child. He HATES to hold hands, everything has to be done by him w/o anyone else's help, and he likes to bolt at the drop of a hat. We picked up the Monkey Backpack from
Walmart for about $10 and it was really a godsend. Ds had the independence he needed and we had the peace of mind that we wouldn't lose him!
9. Id Bracelets - Many people use the IDs for shoes or tattoos but I liked the
silicone rubber bracelets the best (especially when wearing
Crocs or sandals!). Dd wore hers on her wrist but we put ds' on his ankle. I ordered 4 (a back up for each kid) and paid only $12 including shipping. They arrived in less than a week.
I'm sure I'll think of more!