Okay, so this is a little picture heavy, but I need lots of pictures and this way I will be sure not to leave anything out!
First, you need 28 juice bags for a purse without pockets.

Cut a whole in the bottom of each bag, rinse and let dry.

I use double sticky tape to keep the bags from slipping when I sew them together. I have use all kinds and Scotch- permanent, double sided tape is the best. I like the 1/2 inch width.
First I tape together two bags, over lapping about 1/2 inch like this:

Repeat 8x (you need 8 of these). Sew together with a zig zag stitch.

Tape 4 of these pairs together, side by side, I usually overlap about 1/4 in here. Zig-zag stitch.
Repeat with remaining 4 pairs. You should have two pieces like this:

Pleats- I folded over about 1/4 in. pleats - Left to Right: near inside edge of first bag, at straw whole on second bag, at straw whole on third bag and at inside edge of fourth bag. Pleats should be folded towards the center of the bag and stitched one at a time. Repeat on second panel trying to match width of first panel.

Find something round, like a small plate, to trace curved edge on bottom corners of one panel.

Put wrong sides together and zig zag stitch starting on one side of bag, following curved line you drew at corners all the way around to other side. Trim corners outside of stitches.

Sew five bags together in a strip, fold in half and place around top of bag.

Stitch yoke (I think that is what it is called) to top of bag (still zig zag). This is the hardest part, really. I could not do a continuous stitch all the way around since the bags are pretty stiff. I found what worked best was to do the side when the pieces overlapped first, as far as I could go without it slipping off the bag, then turn it over and do the other side lastly I did the corners of the bag (where it goes from front to back panel visa-versa)

For the straps, stitch 7 bags together in a strip (These straps are perfect for a kid, but for an adult you might want to make them a bit longer, maybe add a bag or two). Fold over one third of the way (this part requires a lot of tape).

Fold the other side over top of that. Stitch down the top piece like this:

cut this piece in half and attach to bag. Be sure to reinforce the straps, I did two rows of zig zag on each. Ta Da! Your bag is done!