We do a lot of the same that Steve mentioned (Duffel bag & backpack in driver seat). Keeping everything organized certainly will make storing & locating items more convenient. It doesn't look like you have a lot of built-in storage, so limiting everyone will control space and clutter. Using a backpack for clothes & toiletry items helps limit the amount you pack (if it doesn't fit, you don't take it). Have to say, we have gone through several versions of backpacks, and found one with the front access is the most convenient since you can just zip down the front and see everything...opposed to having to dig & remove till you locate what you want).
We went through a couple different versions over the years and are very pleased with this Osprey version:
https://www.amazon.com/Osprey-Europe...07&sr=8-2&th=1
When you pack - pack like you're backpacking...layer. It's Ok to wear some of the same clothing a couple times/days if needed, and you can get a collapsible pail to wash some clothes if needed (just purchase the proper biodegradable soaps).
Remove any redundancy: Each person gets one tumbler with a top that seals well (preferable one that hold cold & hot liquids well), only need 2 cooking pans (we have one cast iron skillet and a medium sauce pan).
We tried a storage net across the bottom of the pop-top bunk, but anything that sticks down more than 6" just seemed to crowd the space - so removed it. If you carry pillows, buy some compression sacks you can stuff them into (clean look and smaller footprint). We only use 4-season sleeping bags (for same reasons).
We use a pelican case on top of the spare tire for added storage (have two different sizes I use; depends on the trip for which travels with us - large and extra large). Normally store some kindling, a Citronella candle, and fill the rest of the space with additional beverages (beer, powerade, etc).
We mostly use our trashoo style bag (attached to rear tire under the pelican box) for all the dirty clothes, and a separate plastic trash bag for actual trash stuffed inside also). Keeps the smell out of the van.
Not sure what counter space you have, but I use plastic ammo boxes (have 5) that set across the top of the counter. They stay in place with 2 strips of 1.5" Velcro across the top of the counter with the other side taped on the bottom of each box. Holds the boxes very well. Strategically, since the boxes can easily be removed we store 'like item stuff' in each one which we use at different camping stages. For instance;
*One holds all our coffee & tea, filters, grinder, and sweetener supplies
*Another a variety of fire starters, long lighters, matches, propane torch head, etc.
*One has all the cleaning & scrubbing supplies for dirty dish's and cookware.
This way, I can just yank a box, walk it outside to the necessary project. Also keeps it out of the drawers.
Many variations of the Trashoo rear storage bags, some IMHO made better, and some made much larger (larger may work better for a family of 4)
I highly recommend the first one (the XL works great for us, but they also have a smaller one - extremely well made!):
https://www.blueridgeoverlandgear.co...storage-bag-xl
https://www.blueridgeoverlandgear.co...re-storage-bag
Have a friend that uses this one (they like that they don't have to dig all the way down into the bag, has a zipper in the middle that goes to the base of the bag)
https://camplolo.com/collections/sto...41013001912479
To mount storage boxes on the top of your spare tire:
https://www.amazon.com/Rock-Slide-En...BoCah0QAvD_BwE
Consider a Thule style storage box for the roof of the van (will keep all your chairs, tubes, etc out of the van)
If you have a trailer hitch, there are many hitch mount baskets you may consider to hold additional 'stuff'.
Our Rear Tire Storage bracket mount:
Picture of our Plastic AMMO Storage boxes on the counter (left side)