Vacuum sealers remove air from packaging, thus eliminating the effects of oxidation, which can cause foods to degrade. From beans in the pantry to vegetables in the freezer, vacuum-sealed foods can stay fresher longer. Vacuum sealing also reduces the volume, so you can store more items in the same amount of space.
This straw method won't be quite as effective as using a vacuum sealing machine, but it's still very useful, and much less expensive. Place your food in a plastic zip-top bag (make sure it's a freezer-safe bag if you plan to freeze) and zip it almost all the way, leaving a small slit to insert a straw. Suck the air out through the straw, quickly pull it out, and close the bag. That's it!
(Note: a plastic straw works better than the paper one pictured above.)
(Images: Emily Ho)