Trolling motors are likely among the most useful options. They used to run $40 at the S&D discount. Came with battery clips to hook up to the 12 volt. I hear they've come a long ways...
Can a trolling motor bring me home if something happens to my primary motor?
I'm assuming you are talking about a freshwater boat, for lakes and streams? I suppose the answer to your electric trolling motor question depends about how far away "home" is, and what the weather is like, when the primary motor conks out. A trolling motor will not build much speed, so your trip had better be short, or you will run out of battery before you make back to the launch.
If you're concerned about having back-up propulsion, a small, gas-powered kicker motor (6-15hp, depending on the size of your boat) is a better solution than an electric trolling motor.
And battery chargers. What do they mean by 2 bank or 3 bank? Edit; Do my accessory batteries need to be charged at home or will they charge from the boat electrical system? My own ignorance abounds...
To keep it simple, think of a 2-bank battery charger as one that will charge two separate batteries, and keep both charging circuits isolated from one another. If one battery finishes charging before the other one, the charger stops charging that one, but keeps charging the other battery. A 3-bank, charges 3 separate batteries.
There are several ways to wire your batteries, so that the outboard charges all of your batteries, when it's running. I really dislike 1-2-Both battery switches. People typically leave them in the "both" setting and wind up with two dead batteries.
I like to have a dedicated starting battery for the outboard, and then a separate house battery for everything else (if you have an electric trolling motor, it will have it's own battery or batteries, as well). An automatic charging relay makes sure both batteries charge, when the outboard is running, but keeps them both isolated when the engine is off. Even if the house battery gets worn down, the starter battery stays fresh to get the motor running and get you home.
Cup and electronic device holders. What are the best electronics for a small fishing/hunting boat?
Electronics are very subjective, and people have their preferences. I run mostly Garmin, because they are easy to use and they seem to last forever. I avoid Lowrance, because I can't stand their customer service, or rather their lack of customer service. Others will certainly have different opinions on the matter, and it's nice to have choices.
Be sure to get a model that is specifically suited to your intended application...shallow water, deep water, GPS, navigation charts and underwater contours. Most river folks (around here, anyway) don't bother with a chartplotter, but if you're fishing lakes and costal areas, having a GPS/Chartplotter is vital.