I was thinking the other day of how some carrier bags are over-engineered. If you live somewhere they cannot be recycled, it seems wasteful to let them go to landfill.Then, when I saw one next to a piece of string, I had the idea for my first Instructable for re-using an old bag or two to make a simple rucksack. This was particularly useful to me as I work in a wetland sometimes and need a cheap waterproof bag that let me keep my hands free.

The advantages of this bag are:
low cost
low weight
small volume
simple to construct
environmentally friendly
water resistant
all parts have other uses

...oh yes, and it actually works, too.

(The only disadvantage is that you look like a tramp!)

Step 1: Get Your Stuff Ready

For my bag I used the following:

2 plastic carrier bags of equal size (the thicker the plastic the stronger the bag)

A length of rope (I used a 4 metre length of 10 centimetre climbing rope; with the assumption that a larger diameter makes the straps more comfortable and the rope stronger, thus more useful)

2 coins (10p size seems great. Alternatively, many other small objects (stones, glass eyes, diamonds et cetera) would also work, but I thought that coins would be simple and useful )

Step 2: It's a Double Bag Job!

The first step in assembly is to put one bag inside the other. The main advantage of doing this is for increased strength and reliability. A further advantage is that you have the option of using multiple compartments; this is handy if you get some of your kit wet and want to keep it separate from your other stuff.

These bags tend to have folds at the bottom corners. It is important that you push the inner corners inside the outer ones as much as possible.

Step 3: Get Knotted!

Push your coin into the first corner and then tie off the rope above it using a fisherman's knot. Pull it tight until the corner fits together snugly.

Step 4: Thread 1st Strap

Start threading your straps by taking your rope up diagonally, then through and across. For example, if you tied off your left corner first, take your rope from the bottom corner and thread it through from the outside of the right bag handles through to the left handles and out the other side. Doing it this way ensures the rucksack tends to be closed at the top. Be sure to go through all of your bag handles.

Step 5: Final Strap & Corner

Now take your rope down to the other corner and tie it off again as you did the first. Remember to use your coin and try to get the remaining rope coming out of your knot the same side as it did on your first, this will give your rucksack a noticeable front and back and make it easier to wear.

At this stage you can try it on and re-tie if your feel the length is inappropriate. Trial and error is a wonderful thing!

Step 6: Tidy It Up

You might have quite a bit of rope left over by this stage, depending upon the length you started with and the size of the straps. To save using tape, I tied mine off every now and then by putting an overhand/Stafford knot around the strap.

If it is long enough to go through the handles I think that this might help prevent the rope from shearing through the plastic at this point. If you've got a lot left over, you may want to tie it off to seal the top of your new rucksack.

Step 7: Use It!

So there it is; now you are ready to saché down the catwalk in Milan with true panache from the trash!

I'm not very good with knots (and can barely keep my shoelaces tied half the time), so I'm sure that someone who actually is could figure out adjustable straps or something equally wonderful.