I have a small net in my BOB, with holes probably near the size you mention, but which is smaller than 12 x 10. It's probably about 4 or 5 feet by 6 or 7 feet. I bouoght it at Walmart but cannot find one on it's site. You cna get something like it here:
http://www.jannsnetcraft.com/bait-dealer-nets/936150.aspxI don't think one net would work for all kinds of fish. What kind of fish would be in the areas you would expect to travel?
I think a minnow net is probably a good choice. It would not be easy to handle a larger net, unless you are using a cast net. A cast net is going to have some weight and need some practice. A minnow seine or an umbrella net requires very little skill. If you do manage to get some minnows, then you will have bait for larger fish. You can also just eat the minnows.