How can I repurpose gallon milk jugs?

Can you cut off the top part and plant some plants/herbs?

Save them for watering your plants with tepid water.

As an avid gardener, I use mine to create mini greenhouses to start my seeds. This is called winter sowing. Keep the cap on the jug. Poke small holes in the bottom of empty jug. Step 2: using the handle as your guide, cut the jug three fourths of the way around, don't cut under or thru the handle. This way you flip the top up. Step 3: Place starting soil in the bottom half of jug. Spread seeds around as directed on package. I use a spray bottle to mist the soil/seed combo. Step 4: Flip the top section of jug back to original position. I use masking tape to hold in place. Step 5: Place container outside in a sunny area. Each day you will need to unscrew the cap and mist thoroughly. If there is too much condensation, you can leave the cap off. Once my seeds have started growing, I untape the jug, cut down the side of the bottom half of jug in order to be able to transplant my new seedlings. I live in Ohio so I start these little greenhouses the last part of March.

Cut them off and use them for storage - they can be decorated - painted, covered with rope, etc. for attractive storage 'baskets' for small items.

Use the top as a funnel for paint etc.

My parents would fill with water and freeze. Whenever we needed crushed ice my Dad would take the hammer and crush the ice in the jug before cutting it open and pouring the ice in a bag.