I am planning a surprise weekend trip at the end of April and have already started packing...AND I managed to fit it all, for 2 adults and 2 children, in a 21" carry-on and our DVC tote bag! We're only going to be there from a Friday night to a Sunday late afternoon, so we really only need 2 outfits, basic travel toiletries, and a pair of shoes (which we'll wear the entire weekend). Keeping the compact idea going, we'll be taking an iPad & iPod, pocket-sized digital camera (plus my DH's iPhone), and some snack-sized goodies. As for a light coat, we'll wear 'em onto the plane, which should deter us from buying any extra clothing for warmth.
The trick to packing our carry-on: roll the clothing (I will fit my girls clothing into 2 gallon-sized ziploc bag and essentially "push out the air" making clothing pancakes). Remember, your toiletries must fit in a quart-sized bag (1 per person, but y'all know that). However, if you're particular about a certain soap, face wash, etc., and you have a rather large bottle at home, might I suggest heading to Target (or of the like) and picking up some empty travel bottles. The next step: ask yourself before putting any item into your bag, "Do I really need this?" I think for 2 adults on a long weekend trip, you should be able to fit everything you'll need into one rolling carry-on and 1 back pack...and technically, each of you are allowed said items, just in case you really cannot forgo that "must have item!"