Here's my list. I'm sure others have lots of tips as well.
Tips for moderate S-days:
1. Plan your treats ahead of time. Go into the weekend knowing what is and is not on the agenda as far as S-es. Pick out something special and nice. (But don't beat yourself up if you depart from The Plan: it's a guideline, not an iron-bound law.)
2. Brush your teeth when you're done (or "done"). This "clean slate" often helps keep things reasonable. With no toothbrush handy I sometimes drink water and make sure to swish to clean out the food taste/feel.
3. Don't deprive yourself. You can't "blow the whole week" because you can't fail on an S-day, and even if you do have some excess in the beginning you will start to scale back naturally (out of habit) as your habits become more firmly established. Do note that when I say "beginning" I am thinking more of years as opposed to weeks or months.
4. Drink plenty of water. This is something you should do every day, but if you're like me it's easier to forget to do so on the weekends.
5. Think about it. Even if you don't create a plan, pause for a moment and decide if avoiding this now will make you feel deprived and give you an "excuse" later to fail on an N-day, or if it's really something you don't want or need. You know your own mind and how it works - use that knowledge. Sometimes you really do want that chem-tacular candy-bar or that second helping of potatoes, and it's okay to have it on an S-day. But other times you don't really want it, you just sort-of want it, or only want it because it's the only thing there. Think things through, and if you change your mind on Sunday, that's okay too.
Hope some of that helps! Good luck at your brunch!