While out and about I always pack a lunchbox for Boomer. Common contents are some rice cakes or rye crackers, some fruit (usually nectarines or a banana), dried fruit (apricots, apple slices), and pieces of cheese. All these types of food travel well in a plastic box and can be fed whilst on the move. Although I would watch out for banana our buggy has a few sticky patches.
Boomer and I are going away for a couple of days (travels including airports, trains and buses) so I there may be a few top tips direct from the field watch this space.