This is what I packed to visit my family. It's also what I packed to visit Chris's family. (Didn't bother unpacking in between). This is basically the same set of stuff I pack anywhere.
It all fits in a single messenger bag, so I never have to check luggage. I don't even use the overhead compartment - my bag fits under the seat.
There are two secrets to make this easy and painless:
1. keep a travel toiletry kit always packed and ready to go. (it's on the far right of this photo). Get the tiniest clear cosmetic bag you can find, and pack it with the tiniest toiletries - shampoo, deodorant, toothbrush, etc.
The tiny bottles will last through a weekend trip, or on a longer trip, they will tide you over until you find a place to buy larger bottles of shampoo and things.
2. bring a laundry bag (a plastic grocery bag will do) and only pack two outfits. Take time to make sure that everything is mix-and-match compatible, and that you have an outfit for every occasion. This is doable, but requires careful planning.
Two outfits for 1-2 people (or three outfits, if you do laundry in your pajamas) fills up one small load in a friend's house or laundromat. If you're away from laundry machines, wash your clothes in the bathroom sink each night (and in this case, pack or buy some detergent and a clothesline). See onebag.com for more info on the wash-as-you-go tactic.