Love all of the suggestions... thanks to everyone who contributed. I'm not going to buy a ton of stuff up-front because I don't want to end up with things I don't actually need...but I compiled a list of the ideas posted above into a giant list because it'll help me remember the great suggestions and others may find it useful. I broke it into a few sections as well
RV Shopping List
Electric/gas:
extension cord
30 amp 50 amp 15 amp adaptors,
Progressive 50 amp EMS
portable gas detector
extra fuses
Plumbing/Water:
tank treatment (e.g. odorlos black tank treatment)
Upgrade sewer hose (e.g. rhino flex)
sewer hose support
Screw on Back flow valve
wand to wash black tank if no black tank flush (attach to above)
upgrade fresh water hose w/ pressure regulator (2)
Water splitter for 2 hoses
45 or 90 degree elbow hook for water hose
Water filter (e.g. blue Camco filter)
storage containers for hook up components / hoses
Rubber gloves for waste disposal
Hand sanitizer for after you take the gloves off ^
Kitchen:
Ice trays or portable ice maker
kitchen utensils / Silverware
stick lighter
coffee maker
coffee grinder
dish drainer
crock pot
forman grill
hand mixer
Paper towels/holder
Plates (micro safe paper or not)
Bowls (micro safe)
Mugs
Kettle
Pizza stone for oven to prevent burning
Nesting Mixing bowls
Measuring cups/spoons
Pots/pans (removable handles are best for easy storage)
Dish sponges
Small dish dry rack (fits in sink for storage)
toaster
electric griddle
Outdoor:
outdoor mat
camp chairs
folding table
table cloths for picnic tables
leveling chocks
exterior windshield cover
grill / bbq
Bed/Bath:
Pillows
Sheets
Sleeping bags
blankets
Electric blanket
Septic-safe toilet paper
toilet paper holder
Command hooks
Shower Squeegee
Shower gel / soap
Shampoo
Upgraded shower head
Air freshener
Cleaning / Household / Life Supplies:
Bleach (need to sanitize lines and tank on new unit and after winterization)
Disinfectant wipes
Broom
Floor cleaner
Glass cleaner
laundry soap
Dish soap
bug spray
sun screen
Wasp spray
Bear spray
13gal Pop up trash can(s)
Batteries
First Aid / Emergency kit
Electronics:
small vacuum
Digital thermostat
Fridge/freezer thermometer
Small ceramic space heater with thermostat (saves propane)
Digital air gauge
Led headlamp
Flashlights
battery operated candles / lantern
dehumidifier
Misc:
New locks to get rid of the generic keys
Tow mirrors (see backup camera below)
Jack or trailor aid for tandem wheels in case of flat
Damp rids/dehumidifier
Step stool for large first step
Quarters for laundry etc.
level or equivalent gadget
Wifi extension
board games for rainy day
maps /GPS
campground directory / app
bungee cords
Tools:
sockets for water heater annode (1 and 1/4 usually), lugs on new rig, WD hitch etc.
Adjustable wrench
Screw drivers
Drill and bits/drivers
Voltage tester (12v and 120) to troubleshoot
Tape measure
Duck tape
Electrical tape
Eternabond roof seal tape
Dicore if you find any holes
Hammer (BFH)
Gasline tape
Teflon tape (annode)
Dremmel tool
Scissor jack bit if you have manual scissor jacks