Here are a few things I've done for our past trips (& we stay moderate, but it seems like space & staying organized with 4 people is always an issue.)
clothes pins for hanging wet swim suits up on the clothes line in the shower
baggies, baggies, baggies! For little kids, put an outfit in each bag. That way they can grab one & get themselves ready. I also use baggies for pressed pennies, pins, change, sharpies (to take to the park for autographs,) bandaids, extra batteries (for our portable fans,) etc, etc.
wire hangers--we fly so suitcase space is a premium, but want to be able to hang up what we can since drawer space is never enough. Our dry cleaner gives away wire hangers. I grab a couple dozen, use them while we're there then leave or put in trash. They don't take up much room on the way there, & don't have to worry about bringing them back.
for bigger kids (when their clothes no longer fit in baggies)--I pack by outfit. Put bottom, underwear, top, socks folded together in the suitcase. Yes, they can dress themselves, but if your child is like my DS, he would rip thru the suitcase looking for each item & would make a big mess in the process.
Last trip I discovered a new solution--the plastic "case" that comes on the sub sandwich Lunchables make for great storage containers. Each of us had one to put our stuff in at the end of the day (wallet, sunglasses, pressed pennies, trading pins, chapstick, etc, etc.) May sound silly, but they were great! Plus, throwing them away for the return trip freed up some space in the suitcase.
pop up hamper--I know this has been suggested before, but make sure it will fit in your suitcase. I bought one based on seeing it suggested many times. Problem was, it was to round to fit in our suitcase. Luckily I didnt' wait until the night before to find this out. Since I couldn't find a smaller one, I used a drawstring duffle bag style one. Hung it across a couple of hangers so it was easier to put stuff in thru the week. At the end of the week, closed it up & put in one of our suitcases. Easier to carry the whole bag to the laundry room when we got home (ugh! I hate that part of vacation!
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Always looking for new tricks & tips so keep 'em coming!