For me it is a very complicated thing. Going from Boater to Non Boater gives you a whole new perspective. As I have a whole room full of tackle, I generally try and take as little as possible. Which is not always possible. For instance I have a 2 day tournament this weekend on a body of water I have never fished. Not to mention the fact that I really haven't had a chance to do any fishing, so with my boaters permission this tournament bag will be my big one.
Holds 5 3700 boxes, I can put 3 bags for soft plastics which hold 10 bags each, and also has room for my weigh-in bag, Spinnerbait binder, spools of line, scale, tools, rain suit, cull Tags, and measuring board. I know sounds like a lot but there is more I also wear a fanny pack while fishing with just a few things I know I'm gonna use such has a couple bags of soft plastics, hooks, weights, Jigs etc whatever I'm catching them on keeps me from moving about the boat and digging stuff out. I also have pliers, scissors and clippers on my fanny pack too.
Now I also have a medium sized bag which I use most often that only holds about half of that stuff, and a small bag I use on my home waters which I know exactly what I need. I'll add pics of my big bag loaded and my fanny pack when I get home in the morning.
No matter what bag I take I keep it under my legs or console "if a dual console boat" while running and in the passenger seat while fishing. Keep your stuff put up and the size shouldn't really matter.