My family does a "Family Morning" every Sunday...cough, cough... Okay, we try to do it every Sunday, but with two middle schoolers and all our volunteering, time doesn't always allow. But when we do, each of us has a campaign that we run an alternating Sundays. With no consist time between sessions, sometimes things are forgotten, so here are a few ideas to keep things straight.
1) Have your players take notes. My youngest was doing that on her own, because she liked to keep track of every time she trashed my adventure, but it is a good idea. Have them keep a spiral notebook or, if they are doing Pathfinder, make sure they take notes on the back of their character packet.
2) As GM, make sure you take notes. As much as I'd like throw out all those monsters my characters trampled once they do so, I don't until I write in my spiral what happened and what treasure they found. I also don't throw out treasure sheet until I know they have picked through it. (Though, I do try to keep track who has what magic items and where they got them.)
3) Do a recap before you start the adventure. Start with what butt-kicking they did last adventure, (or how they got their butt kicked), and answer any questions your players might have at that time. My campaign has my characters looking for some lost artifacts from an ancient civilization so I remind them what info they found the last few adventures and what they are up to now.