Do you really need it, really?
-Anything you MUST have to fly the airplane, to physically stay in the air.
-The idea is to extend the battery power by cutting out all unnecessary items, especially big drain items.
This is not an argument but a thought
-Flaps? you can land flaps up.
-Boost Pump? The engine runs fine without it.
-Transponder? Don't need to stay in the air (live near class B, C nice 2 have)
-Com? Probably a must in most builders books unless you have a handheld
-GPS? Probably a good thing and handhelds have low drain, but also can have their own battery
-Electronic Ignition? A must to stay in the air if you don't have backup (magneto)
-Glass?A big one now, since all pitot/static & mechanical gauges are all-in-one EFIS & Engine Monitors. (Can physically fly without it, but its a must for most).
-Lights? You can fly without lights in an emergency, must land, dark runway at night, Landing lights a must?
The idea is extend the battery.
What do you need to stay in the air?
Don't confuse legal & min necessary to stay in the air.
The idea is extend the battery, for that item or items you MUST HAVE!
Have you ever tested you "essential items on the ground to see how long they last on battery power?
Autoengines with electronic fuel injection and ignition are the most demanding. Since the engine is so electrically dependant you may NOT want to have the EFIS as essential if you have backup mechanical/pitot-static instruments.
I see essential busses with everything on it, why? (especially if you can individually turn off individual items).
The question is DO you need an individual essential buss at all?
Why an essential buss, just turn stuff off you don't need when you want to conserve power. If you don't want to use, lights, flaps and boost, leave them off. (Not recommending this, but I know a guy in a Cessna that flew freaking 1/2 way across the US but turning everything OFF, wet compass, map, airspeed, altitude and watch. Piper J3 has no electrical system. I think the first goal with the electrical system is make it NON-essential if at all possible.
Food for thought to simplify wiring. Our planes are mostly day VFR (most fly day 90% of the time) and we are wiring them like a B737. Nothing wrong with it, but....
Keep it light
Keep it simple
Keep it per plans (has advantages)