If you wanna save as much space as possible with all of your bags or barrels or whatever else you use for recyclable materials, save yourself some storage space and time with this nifty and easy little method. I'm not taking originality credit for it, but it's useful for everyone Green out there.
Step 1: Prepare
First, grab yourself a bottle with the cap still on it.
Unscrew the cap as far as possible while it is still on the threading. This is to let air escape easily from the bottle and also keep it compacted afterwards.
Place your palms on opposite ends of the bottle, being sure not to screw in the cap anymore.
Step 2: Do It!
Squeeze your hands together evenly so that the bottle collapses on itself.
Once it is as small as it will get, screw the cap tightly back into place with your palm. This is to keep air from re-entering and preserve the now economical size.
Step 3: Practicality
By using this method, you will be able to get each bottle to at least 1/4 of its original size! Yes, certain plastics will not crush as easily (looking at you Gatorade and Propel), but even these can be slightly reduced in size. This technique even works on liter bottles, but a little more muscling is involved.
Anyways, enjoy the new found space you have!