Drink tap water whenever possible. Avoid bottled one and soft drinks.
Buy just enough perishable goods so that they are used by their expiration date. Avoid buying too much and having to throw them away after their expiration date.
Prepare food yourself. Don't buy deeply processed food, since it consuming evolve unnecessary warm/freeze stage.
Take food with you from home to work in reusable container if you could. This will reduce amount of transportation if you don't have place to eat in walking/biking distance and also reduce amount of waste on packaging/thrown away kitchenware.
Buy locally grown food. This will reduce transportation toll on environment
Buy organic food if you have such choice. Organic food production doesn't allow usage of chemicals pesticides, herbicides, fertilizers.
Buy seasonal fruits and vegetables.
Reduce meat consumption. Meat production is ineffective way of producing food and also cause pollution with manure, methane as green house gas. Industrialized meet production also means animal cruelty: animals are not raised in natural environment; in many cases they are not feed with food they used to consume in nature; animals are not allowed to follow their natural instincts and kept in small space.
Plant vegetables and fruit tree if you have land to work on. Some folks even grow hens for eggs and meat in city!
Explore your neighborhood area for fruit trees on public or abandoned land to peek fruits. Sites such as http://cityfruit.org are good resource for finding such trees nearby.
Give away your excessive vegetables or fruits harvest to your friends, neighbors, colleagues, community.