Actually, Jack's being conservative.
To actually cook, instead of warm, food, you're looking at a hotplate in the 1000w+ range. There are smaller versions, of course, but they will not be as hot and will thus take longer to cook.
I'm not aware of an actual 12v hot plate that will do more than warm up stuff, but assuming you could find one at 1000w then you'd use about 42 amp-hours for every hour the plate was in use. That's 42% of a 100 amp-hour battery.
Given that it's bad on batteries to draw them below 50% of capacity before recharging, that one hour of use pretty much is it unless you have solar power, shore power, or more battery. Hardley anything left for the refrigerator (which draws about this itself each day, give or take, lights, pumps, music, TV, etc).
If you run a 110v hotplate through an inverter, it's even worse because of the conversion loss and draw from the inverter.
I'd like to suggest that if you are dead-set against propane (or diesel, if you are buting a diesel SMB), you look into a portable butane stove. The canistes are not dirt-cheap, but you can cook for a weekend for about $1.50 - $2.00 per hour (S.F. Bay Area prices).