I'm definately not an expert but did research some of the same questions when trying to determine "what size battery bank" to put on my build. I was looking for "how much" to last a couple of days of cruising without having the option of plugging in somewhere to recharge.
You can keep your "needs" low with today's LED lighting. It's quite a bit more expensive, but all your nav/interior lights will draw next to nothing (like 1 or 2 amps total for the day).
Likewise, simply check the specs on your fishfinder/gps - probably draws about 1 amp max or so - so maybe 10 amps on a really long day out.
I would suspect the radio would have a similar power draw.
Other items are the "power hogs".
If you are talking an electric stove - you better add a barge for the batteries - just not practical - stick with alcohol or propane.
The shower - are you considering with "hot water"? A water heater needs generator power - you could run a waterpump on battery if you don't mind cold showers
And the plug for the laptop. Again, depending on it's requirements you could go with a simple up-converter (75-300 watts) from most automotive discount places. The thing to remember is when converting to AC from DC, you need 10X the DC.
So, to get 75 watts out @ 120, you need 750 watts in (that's 62.5 amps @ 12 volts) - however, since most laptops run on "converted" power anyhow, you could probably simply run a DC-DC adapter.
Ultimately you need to make up a chart of everything you plan to run and how long you think you will run them (then add 25%).
If you come up with say 100 amp hours for a 24 hour period (or 48 hours, or whatever until you can fully recharge), you almost want to call that 200 amps (so you don't overtax the batteries and really shorten their life - most mfg's don't recommend more than a 50% discharge on a regular basis).
I also took a hard look at "alternate" recharging sources. The bottom line is, unless your power usage is very very low, you probably can not recharge with wind or solar alone.
Take a fairly large (expensive) solar panel producing 100 watts (most produce quite a bit less). That's about 8 amps. So even under perfect conditions you might get 60 amp hours worth of charging from it.
Likewise, I priced out the portable wind Turbines that advertise 400 and 600 watts (33-50 amps). But that is running full tilt. At most cruising speeds, even into the wind, 200 watts was almost wishful thinking (15-20 amps). I tried to balance the almost 1000 dollar cost (turbine, mounts, controller etc) plus the "running" at 20 mph for 5 hours, to replentish the maybe 100 amps a day I would suck from the batteries.
If you can keep your power requirements to an absolute minimum and you have deep pokets to buy the best solar/wind products currently available, you probably can do it.
However, at the current time, it's still tough to beat a super low end 200 dollar gas generator and a couple bucks worth of gas. It can recharge a 200 ah battery bank in a few hours and it doesn't care if the sun is shining or the wind is blowing when it does...