I've read some about what to bring as a Co angler but I wanted to know what yall pack and how ya pack it.

One tackle bag with 4 3700 boxes, some favorite soft plastics in front pouch, 4 rods enough?

Bag doesnt have much room for a couple 16oz drinks or sandwiches. I think a tackle bag and backpack would be too much.

I used to carry a bag that held 6 3700 boxes and my essential plastics. Bass boats are all equipped with built in coolers and I've never had a boater who wouldn't let me put my lunch and drinks in their boats cooler, although I did have to buy my own ice once because my boater didn't bring any food and had a water jug that he drank out of but that wasn't a big issue for me. I tried to limit myself to 6 rods, which should be enough on pretty much any occasion. 

I bring a duffel bag which can hold 5-6 3700 boxes. I usually bring 5 rods, a soft bait binder is a great investment aswell.

6 rods sometimes seven.  4 is enough. You can always bring extra reels and not extra rods.  I use a medium Patagonia Black hole duffle bag as a tackle box. it holds 6 3700 plus has room for food drinks other stuff i may want or need.  probably more than what most bring but i own more than most and like to have my basis covered when money is on the line. Bring a save Phace if it's cold, good Smith optics photochromic polarized glasses, a balance beam, a ruler, i bring a little livewell treatment sometimes, rain/cold gear if you will need it, life vest such as the Spinlock Deckvest Lite.  Dont forget your pliers, scissors etc and $40 for your boaters gas.  I'm probably msising things.

Oh yeah rod gloves and lure wraps will save you a lot of hassle because all of your rods will be buched and tangled together.  No bass boat has a good system for co-angler rod storage.  At least none that I've seen and this includes $70,000 rangers.