Wastefulness is a habit of using things carelessly or recklessly. To combat wastefulness in the cafeteria, your environmental club might develop a proposal for composting uneaten food and reducing the use of paper napkins.
Wastefulness takes many forms, from leaving the sink on while you slowly brush your teeth (which wastes water) to lounging for hours in front of a mindless TV show you don't even enjoy (which wastes your valuable time). There's also the wastefulness of a company overpaying for office supplies, or the extravagant wastefulness of a lavish party with ice sculptures, chocolate fountains, and piles of expensive food.