I'm in no way an "expert" on traveling with small children. But I do have to say that after traveling successfully on 4 airplanes, in a minivan for 4 hours with no mounted DVD player, in two taxis, and on a monorail, I may have a few tidbits of advice to offer you all.
So, in no particular order...
1. Invest in a portable DVD player.
2. Go to the Dollar Tree and get a cheap CD case. This is where you can store all your kiddie DVDs in one place and get rid of cases (and extra weight).
3. Replace your pocketbook and your diaper bag with one backpack for traveling.
4. Have lots of snacks in individual containers/ziploc bags already portioned out (and if they accidentally spill the bag, it's not the entire bag).
5. Bring about 5-6 take and toss plastic sippy cups with you (and make sure you hide them in your room because housekeeping will take the "toss" part seriously).
6. If flying, pack a carry-on bag with extra clothes for all of you- and plenty of diapers and wipes.
7. Also if flying, when taking off or landing encourage your child to constantly do one of the following, depending on age: suck on paci, drink juice or water from a straw or sippy cup (the flight attendants will fill up your sippy cups when you enter the plane and ask nicely), chew gum, or suck on a ring pop.
8. Keep the kids on a schedule the best you can. Kids thrive on routine and will be much better socializers if they have had their regular nap and have kept a semi-regular bedtime.
9. If changing time zones, give it one day for each hour to make the full adjustment. Try and shift one hour a day.
10. Just because it's vacation does not mean that vegetables and fruits cannot be consumed.
11. But ice cream is an acceptable dinner one evening.
12. If flying and going through security, wear shoes that slip on without socks. It is crazy enough without having to tie dozens of shoe laces.
13. Don't pack more suitcases then you can lug around yourself (and/or fit in your vehicle).
14. Keep cash in small bills on hand for tipping.
15. Wear pants with button pockets.
16. Check out if your hotel has laundry facilities and then you can pack half the clothes. (And if so, pack a roll of quarters.)
17. Reserve your porta-crib in advance.
18. Request a bathtub for your room in advance.
19. Share meals when you can. It's way more economical and also allows you to try new things when in new places.
20. When flying with a baby under 2 for free bring something to put between the seats so they can sit between you and have "their own seat." We used a memory foam bath mat from Target (see tan thing below). It basically makes it more comfortable for them and eliminates the "crack" between the seats.