I don't recommend that you bring your own travel crib or play yard. Most hotels have decent pack n plays. I recommend that you bring your own play yard sheet and some anti-bacterial wipes. I cleaned the thing down then put our own sheet on it. Our son slept great, well not as great as usual. At home he sleeps on an incline due to acid reflux, but he did well for being flat on his back.
If you have an infant I highly recommend a Snap and Go style stroller. This is basically a frame that the infant carrier/car seat snaps in to. I like the Clic It by Safety First because it has a HUGE basket, two cup holders, a snap-close storage by the handles, and a stretch canopy for sun and rain protection. The other big bonus is that it is very light weight. I am able to close it one handed. It fit in the back of the tiny car we rented. We have a Peg Perego 30/30 infant carrier and this was the frame that it fits in properly. I believe most major car seats will fit this frame.
I recommend bringing a bath tub that inflates. I blew this one up in about 15 minutes, yes it took a while but I really like the thing. It has two compartments to hold soap, washcloths, etc. There is a back rest as well. Another great feature is that it has a suction cup on the back to hang it dry when you are done (see the photo on the right, below)
Brica Bath & Nursery Tuck Away Tote
We used this bright green tote to store our son's bath towels, wash cloths, shampoo, etc. Its light and portable. Folds up and zips closed so nothing falls out!
If you plan to bring a stroller or car seat and want to check it at the gate (not with regular baggage) I highly recommend these. Get the double stroller size even if you have a single stroller. If you buy the single stroller size you will only be able to fit an umbrella stroller. It will keep your things in good shape. Our bags came back with some scuffs but Im glad it was just the bag and not our belongings! It also makes it easier to spot your things and easy to carry as each bag has a carry handle. My husband carried the stroller and car seat gate check bags (full) while I carried everything else plus our son!
If your child is over one year old and over 22 pounds, he or she can use a CARES harness on the plane. Its the ONLY harness approved by the FAA for children sitting in an airplane seat without a car seat. I highly recommend this device. It is small enough to fit in your purse, but will ensure that your child is secured in their seat for flight. It works like the 5-point harness on their car seat. See the link below for more details.