The only way is to do the calculation. Look at each item that you want to use and find out what the consumption on 12v is (wattage). Now work out how many hours each device is on for, multiply by the wattage, and total up that lot (giving you the total number of watt hours you consume). Now divide that by 12.8 (voltage of fully charged battery) to give you the number of Amp hours (what battery consumption is measured in). Your battery will be (say) 100 Amp hours, and you should not discharge it lower than 50 % (so in the example 50 Amp hours).
If your daily consumption is greater than the 50% number above, you're unlikely to beable to get enough in from a solar panel, if it's less you can make some rule of thumb assumptions... do your sums, and post back, then we'll look at the solar side of the equation...