Many of us care about the environment, but it's hard to know exactly how to celebrate Earth Day. Bake a "Happy Birthday, Earth!" cake? Buy the earth a present? (What do you gift a planet that already has four oceans?) To help, we've identified four Earth Day activities you can do to give the globe an eco-boost and reduce your carbon footprint.

Spend the day biking or walking

Potential Earth Day Activity: Find a local walking tour and spend a Saturday learning about your town without burning a single fossil fuel.

Why it helps the environment: It should go without saying that refraining from driving your car reduces pollution and greenhouse-gas emissions. But it's doubly helpful if you live in a large city with a lot of traffic. Consider that the more you sit in traffic congestion, the less efficient your car's fuel consumption become, and the more CO2 emits. All the more reason to make biking or walking to work a daily habit, not just one of your Earth Day activities.

Donate food

Potential Earth Day Activity: Ask your local food bank or pantry about what items they need and get your friends to chip in to help.

Why it helps the environment: Instead of allowing uneaten food to go rotten and increasing the size of our landfills, donating it to a food bank or food pantry ensures it gets to people in need. Unfortunately, uneaten food evenually emits methane, one of the worst greenhouse gases, said to be 86 times more potent than CO2. It's one of those things to do on Earth Day that isn't just good for the environment—it's good for humanity.

Go meatless—and eat locally

Potential Earth Day Activity: Find a vegetarian or raw-food restaurant that sources their ingredients from regional farms.

Why it helps the environment: Generally speaking, raising lifestock is far worse for the environment than growing produce, due to the large amounts of food and water those animals must eat and the pesticides required for the animal's feed. A study from the Environmental Working Group showed that your average piece of red meat was responsible for as much as 40 times the carbon emissions as an equivalent vegetable or grain.

Revamp your food storage

Potential Earth Day Activity: Walk to the store and pick up a resuable bag or container that you could use for years.

Why it helps the environment: You might not even think of it, but everytime you use a resuable container for food storage or a reusable bag for the grocery store, you're helping the environment. Having a reusable container encourages saving leftovers, which means less food in a landfill. And reducing your usage of plastic bags—which can take up to 1,000 years to degrade—can make your trips to the grocery store more eco-friendly.