Make a plan.
By now, you probably have a pretty good idea what your weekend is going to hold. Yard work, grad parties, a trip to the beach.... whatever it is, that is the context in which you are going to be practicing your mindful eating.
Knowing that means you can make a flexible plan to work on mindfulness in those situations.
Lawn work and a grad party? Don't work all day without taking time to eat, only to go to the buffet at the grad party and over eat! Plan to eat a meal or snack when you get hungry doing yard work so you aren't starving when you're presented with all those available party food options.
Same thing goes for heading to the beach. Sure, you don't need to reflexively snack on chips all day -- let yourself get hungry but not so starving that when you leave the beach you drive straight to Sherman's and order the biggest ice cream sundae on the menu. That isn't a good recipe for mindfulness.
In this particular case, failing to plan is the the same as planning to fail.
Make your plan and take the 2 minutes and write it down! Handwritten or typed, doesn't matter to me. Just get it on paper. It will solidify your weekend plan more than just roughly thinking it in your head as you're reading this post. Then, once you've got it on paper, take it home tonight and tape it to your bathroom mirror -- just for the weekend. So you can be reminded of your plan and work to achieve it.