I took the OP to be about snacking between meals not actual meals though some families don't sit down to breakfast together & everyone just grabs on the go, but you could eat when the person you are visiting....most families either eat together or eating with the person you are visiting is normal. Helping yourself to something between meals unless your friend does or the family states "we have xyz snack foods you can help yourself to" would make me feel feel uncomfortable.....like looking through closets, looking through cupboards just as much of a not appropriate thing to do. Besides if they keep money stashed in a cupboard & some comes up missing even though you didn't do it.....seriously messes with trust issues IMO.