Recycle them.

You can put stuff in them then they won't be empty. I use gallon milk jugs as a slow waterer for potted plants. Slow watering lets the water go all thru the soil instead of just running on thru, but it is boring standing there slowly watering them.. Poke a hole in the bottom corner opposite the handle. Use a nail or an icepick(if you can find one) Fill the jug with water or compost tea, ( hold your finger over the hole cause it'll drip) a hang by a string thru the handle over the plant. You can go off and do sumpin else now. You'll have to learn by experience how big a hole to poke, how high to hang, and such. The jug will spin, with a big pot no problem, smaller pots you might need to brace the bottle or run another string off to the side. half gallon works too for smaller plants Here's another somethin I just did with some empty gallon milk jugs.You need a black marker that will mark on the plastic, Sharpies work, masking tape,string, white plastic garbage sacks, a glow stick, a hole poker and possibly a bambboo skewer. This time poke a relativly large hole in the bottom corner below the handle. If you look on the sides opposite the handle, you might see a circle or even a circular depression on one side, color that circle in with the marker, draw and color another circle on the other side. The molded circle is just about the same size as the inside of a masking tape roll, so use that as a template. Poke a string thru the hole you made till it comes out the neck of the bottle,( this is similar to pushing cooked spaghetti thru a key hole.) tape the string to one end of the skewere or sumpin similar and push that on thru like you were sewing. Un-do the skewer and tie the string to a glow stick. Pull the string on back thru the poked hole. Its a good idea to tape the string to the jug close to the poked hole till you do the next step so the glo-stik doesn't fall out taking the string with it. Take the jug lid or cap in one hand and reach way up into to the center bottom of the trash bag and snap or screw it onto the jug, trapping the bag between the lid and jug. Hang your ghost from a tree branch or a rope stretched between two trees. Use black string or yarn and they will really loog like they are floating. On Halloween undo the lid and bag and activate the glow stick and reassemble. You don't have to use a black marker, the eyes don't have to be round, don't forget a mouth, you can tie the bag to the handle or even use strips of cloth. You don't have to use glo-sticks, depending on how dark your yard is, but the glo-sticks really look eerie.You can take a clothes hanger, poke a small hole in the bag and work the hanger hook thru the hole and into the jug handle to spread the bag, but usually they stay spread enough , especially in the wind.You can use other kinds of jugs too Later you can use the bags for their original purpose, mebbee tape the hanger hole if you used them, use the jugs as waterers, cept the hole is in the wrong place, but putting it on the handle side makes the spook look down. You can set the wrong cornered jugs in the garden next to seedlings or even larger plants, prop um up on stones or somethin so the mud don't clog the hole and fill them with water. We had water restrictions last year and couldn't water our gardens unless we stood there the whole time actually holding the hose. I could fill a bunch of jugs in a hurry then let them slowly water my plants, the 'water cops' let me get away with it cause I watered right where the plant needed it and controll the amount each plant got. Course I had a garden full of jugs. I told the neighbors i couldn't afford the hi price of milk and was growing my own.Next spring I am gonna plant beer.