Best to keep it in the original packaging, even if open. This way, anyone having a look can quickly see the ingredients.
Don't worry too much about finding suitable food. Most pet food brands are manufactured and marketed globally by multinational corporations and available pretty much everywhere in the world.Especially in Europe, you'll have no problem finding the same food that you use in the US if you use a big-name brand like Purina (made by Nestlé), Whiskas (made by Mars) or Hill's (made by Colgate-Palmolive).