I did this when my son was 3 months. Here's how I did it:
1. ask your hotel for a room with a fridge. Most will give you one for free upon request, though some may charge you a little extra.
2. Bring a hard-sided cooler and a few ziploc freezer bags (gallon size) for ice
3. Bring your breast pump. I personally recommend 2 - one hospital grade or nice double (Ameda Purely Yours or Medela PIS) and an Avent Isis hand pump for travel.
4. Bring many freezer bags - enough for 4 days worth of milk.
5. Bring a small bottle of dish soap for washing your pump parts.
Shoot to pump every 3-4 hours during the day. Use the double pump when you can, but otherwise the hand pump works fine. You can even do this in the bathroom in a pinch. Use a ziploc bag filled with ice (love those hotel ice machines) in your cooler to keep things cold during the day while you're out and about. (I actually also brought a little soft-sided travel lunch cooler for during the day when I was away from my hotel room). Put your pumped milk in bags and into the travel cooler during the day. Put all into the fridge when you get the chance.
When you travel home, pack your small hard-sided cooler (I used one of those Igloo Playmate) with: ziploc full of ice, then all the milk bags (could also be in another ziploc), then another ziploc with ice. Tape shut, put your contact info on, etc. Check this as a perishible item and tell the baggage check people that it's breastmilk. I flew United doing this and they made sure it came off the belt first!
If the flight is long and you need to pump on the plane, you can always ask the flight attendent for some ice and make sure you bring an extra ziploc bag for that.
It can be done. I brought back over 60 oz, and recently my sister flew with over 100 oz! Worst part is missing your baby!!
Edit to add this comment: It's not the end of the world if you need to dump milk. After all, this is a FREE RENEWABLE resource! I think we (moms who pump/breastfeed) tend to get a little overly protective and anal about our saved milk. Yes, it's wonderful for our babies. Yes, it's "liquid gold" and all that, but seriously, who's counting the difference between 100 and 110 oz of milk? Just do your best and try not to stress about it. Main goal of pumping is to keep your supply up and keep your boobs from exploding :)