The customs requirements for each country varies. You will need to check what each country allows, or not. Generally (very generally) most countries allow pre-packaged snack items such as protein or granola bars, chips/crisps, pretzels and the like. Generally – fruits, veggies and meats are not allowed. Again, this is general, and each country has it’s own customs and food laws. Best to simply check each country’s customs website rather than rely on “advice” from a travel forum.
Enjoy your trip.