Bringing things along that you can throw away will lighten the load on the return trip.
An old pair of sneakers ready for the trash work well for going to the beach.
Use travel size tubes of toothpaste or tubes that have enough left for the length of your trip.
An old pair of jeans ready for the trash can may be fine for one last day at a theme park.
These items that you only have to pack for your outbound journey will provide room in your luggage for your travel purchases to get home.
I'm sure others can think of more.

Jay