Prepare solid when going out

Hi mummies, when baby has start solid at 6 months, if we’re out, how do i pack baby’s food or do i just give those packed purees/baby food available at stores ? Example if we have a homemade food like porridge, i need it to last till nught, can i just put in those food thermos ? Or itll go bad/sour after few hours? Im a ftm and im so confused about baby’s solid. And for 6 months, how often to feed baby solid? Like is it a must to feed during breakfast lunch and dinner ? Or its actually up to us when we want to feed ? Cause their main source is still milk.