Donate blood (Official U.S. Navy Page / Flickr Creative Commons).

Studies have shown that people who regularly help others have better health than those who don't, and that elders who do volunteer work may live longer than those that do not.

ALSO SEE: Nice People Are Happy People 

Here’s your mission for the third week of December:

Sunday: If you live somewhere where it snows, shovel snow for a neighbor. Maybe pick someone you know who might have a hard time shoveling snow out of their driveways. 

Monday: During your lunch break at work, put on a Santa suit and hand out candy or small gifts to your co-workers. They’ll get a kick out of it, and you’ll feel as beneficent and jolly as Santa himself. 

ALSO SEE: 31 Days Of Giving: Week One 

Tuesday: Tape a bag of change to a vending machine for someone else to use. Make sure to leave a note so that people know they can use it. 

Wednesday: Donate your blood. Those who regularly donate their blood lower their risk of heart attacks, strokes, and cancer. “Donating blood can lead to a decrease in blood viscosity, which can lead to a lowered risk of cardiovascular disease,” said a Kaiser Permanente nurse. You could possibly save the recipient's life, as well as help out your own.

ALSO SEE: 31 Days Of Giving: Week Two 

Thursday: Fill out a positive comment card for someone who gives you good customer service. It will make the sales associate smile and make them look good in front of their boss.

Friday: If you live somewhere where stores are obligated by law to charge people for bags, pay for the bags of people behind you. Some people force themselves to carry their newly purchased items back to their car just to save a few dollars on bags. Neither the sales associate nor the customer likes getting in to this situation, so you'd be making the transactions behind you go a lot smoother.

Saturday: Plant a tree in memory of someone. Organizations such as the National Forest Foundation will plant a tree in honor of someone you love for a small fee. Not only will you make someone smile with your gift, but you will also assist in the restoration of the environment.