First and foremost: You're CAMPING!
Keep it simple! Spend your days playing on/in the lake and the evenings outside watching the stars. You're used to camping (scouts), so keep to that as much as possible and leave civilization (and all the gadgets) at home.
Propane will be fine for 3 days - don't worry about that at all.
Electrical - supplement RV lights with LED puck lights, lanterns, etc. Skip the electrical appliances. Try to go without the generator as much as possible - the less you're dependent upon it, the easier camping will be. I have a group 31 AGM battery and can go 4 days without putting a dent in the power - and that's with the water pump on 24/7.
Water - use the campground bathrooms when convenient and RV bathroom during the night, etc. Skip the showers, it's less than 3 full days, use baby wipes and the lake instead.
Really, Friday night to Sunday morning is only 1-1/2 days. You should be fine without much effort as long as you don't bring the hair dryers, coffee makers, etc.
Once you get used to dry camping (campground no hookups), you will be more comfortable boondocking (no campground no hookups). Remember, if you're in a campground, there is someone around who can help you out if something happens - no biggie.