I would not even consider running a 3-way fridge on 12v without the engine running - regardless of how long you estimate your shopping will take. They are absolute pigs on power consumption! Up to 13 amps! What if you take longer than you expected and forget about the fridge - hey, it happens. A solar system would have to be pretty darn impressive to make a dent in that drain regardless of weather.
Derb. 2017 Colorado LTZ 4 x 4 Auto. 2014 Southern Star 720 and 1980 Zephette 340. 2 x 100 a/h AGM. 3 x 150w solar. Ctek D250S-Dual controller/MXS15 charger.172L fresh/grey. Diesel heat. RMD8555 fridge.