Rule #1 for packing -- overpack, then subtract.
When I travel, I pack EVERYTHING that I am taking with me into my Main bag. This includes my coat, shoes, laptop case, cameras, etc. Once it all fits, I take out my carry on stuff, which then leaves me with my main bag only partially full. But this leaves me a lot of options:
1) At security (on a carry on trip) I scan two items -- my laptop and 1 bag (where I stowed my coat, shoes, watch, keys, cell, etc.) I get through quicker and get hassled much less
2) In the terminal, its much easier to haul one bag around.
3) If I checked the bag, once I pick it up, I "refill" it with the carryon stuff -- once again, 1 bag.
4) If I do some shopping, I can adjust my packing easily without the need to add more bags
Also, my backpack is a carry on, and my main bags are always rollers.