First off let me start by saying I was a full time breast feeder up until my daughter was 9 months old and I got pregnant again. I loved it and plan on doing it again with this next baby! However I know the advise I will give is not popular among the crazy dedicated breast feeders out there...
I went on a trip to run a half marathon when my daughter was 4 months old. While on that trip I pumped whenever I could, but for sure just pumped and dumped. Too hard to store and make sure I was keeping at the right temp. If you don't pump while gone, your milk will decrease for your baby when you get home. I also did not leave breast milk for my husband to use. He used formula for the 2 days I was gone... that is the unpopular part. :)
We started at 4 weeks giving her ONE formula bottle a day. Usually the one right before we put her to bed at night. It seemed to help hold her a bit longer and we could get a bit of sleep. We also did this (upon the recommendation of my lactation consultant) because I needed to know that if I HAD to leave in an emergency or someone needed to care for her she would be used to the taste of formula as well as a bottle nipple. I am SO glad we did this!!!! She didn't like the bottle nipple at first, but we started off with breastmilk and in a day or so she was cool with breast or bottle. Then the next week we moved to formula and again she did just fine.
You will see that as much as breastfeeding is the best thing you will ever do it is also the hardest! Babies don't get it right away and we certainly don't know what we are doing. But stick with it and it WILL get better! However knowing my daughter could take a formula bottle took a burden off my shoulders, in a sense, allowing me to know she would be fine if I had to leave... I know it was more mental for sure, but it sure put me at ease. And although we breastfeed ALL the time (I was a feed on demand mom) and even out in public, it was just nice to know a bottle could be used if need be. Plus my husband could have his time to bond with her as well....
So if you choose to use some formula here and there please don't worry about it and if for some reason breast feeding doesn't work for you at all, please know your baby will be just fine on full time formula. So many moms are made to feel bad about this choice, but sometimes it is better to be a happy mom then a miserable breast feeder. So many of my friends were made to feel shameful for the fact it didn't work for them and those mothers that did that to them should be ashamed of themselves...
Anyhow good luck on the trip... no matter what you do it will all work out. Funny thing is that what you plan on doing now will most likely change once that baby is born. Funny how they tend to alter our brain and make us change up everything we thought we knew! :)