We have a variety, too.
For family plane trips with good (read: private, door to door) transfers we have a big suitcase on two wheels. It usually packs full between 20 and 25kg, so it sets its own weight limit.
By myself I would never take anything other than a 50L backpack. Everything I need and so easy to skip, hop and jump from one place to the next (especially when running late). Can go carry-on with some airlines, too. In fact, with a family holiday (including nappies) it usually ends up being used as carry-on or overflow (and sometimes also day pack).
We have a trunki for our carry-on with the kids when doing air travel. The trunki usually contains all essential items (sometimes including the nappy wallet, sometimes not). Once on board the essential items can be accessed more easily and the just-in-case items left overhead.
If doing air travel without nappies, we have a smaller carry-on backpack/daypack. Sometimes this is our boostapak if we need it as a car seat at the other end.
My husband has a second backpack 70-80L for camping trips. It used to go hiking but we haven't been game to do a long hike with the kids yet, so a smaller pack has been sufficient for that so far.
My husband has a smaller suitcase on two wheels which he uses for business trips. It's small enough to go carry-on, but big enough to carry a week's worth of everything he needs. If doing a winter family holiday we sometimes use this as a second suitcase. Or if a summer holiday with poor (I shouldn't say "poor" as these are my favourite type: public, station to station) transfers (especially if we are covering lots of destinations and taking eg trains or buses between) we use this together with a backpack.
I also have a laptop backpack which I used to use for carry on or overnight trips back when I had little enough to carry that an extra laptop wasn't a huge hassle. It now mainly gets used as a normal laptop/nappy bag around town for those occasions I want to take a laptop somewhere - but this is rare.
I also have an isoki nappy bag that can be used as a soft overnight bag.
Edited by beabea, 16 January 2013 - 11:49 AM.