This pattern was once found at http://www.abc.net.au/sydney/simonmarnie/img/bagpattern.jpg but that link is no more. This is a wonderful pattern and I make my grocery bags from it. I've cached the image here because I know it will be useful to others. More info below.
What you'll need
Yes, that's very tiny thread and a tiny hook, but don't worry, this bag will not take you forever to make. It's fairly simple and makes a good bus project.
My modifications: I don't make the drawstrings or the brass ring. Just not needed. I make the regular size (not the large option). I make the handles differently, by working about 15 rows of long treble crochet that are 4 stitches wide.
I find size 10 thread the best size (it's also the easiest to find at any
craft discount store) but you can make this pattern with a different size thread and hook if you
like. Knock yourself out!
(Reprinted from above. "ltr" = long treble crochet (wrap 3 times).)
Make a ring of 12 chain.
1st Row: 12 dc into ring.
2nd Row: 1 ch, 1 dc into each st.
3rd Row: 1 tr into each ch and dc in previous row (making 24 sts)
4th Row: * 1 ch, 1 tr, once into 1st and twice into next st. * Repeat into the 24 sts (making 36 loops).
5th Row: 2 ch, 1 ltr into each loop.
6th Row: 3 ch, 1 ltr into each loop.
Next 3 Rows: 4 ch, 1 ltr into center each loop; at end of row 9 put only the 4 ch into the last loop.
For Beading. [in other words, this makes a railroad-looking casing to thread a drawstring through]
10th Row: 4 dc into each loop.
11th Row: 5 ch, 1 dc into end st of each loop.
12th Row: 4 dc into each loop.
Next 4 Rows: 8 ch, 1 dc into center each loop.
Next 4 Rows: 12 ch, 1 dc into center each loop.
Next 4 Rows: 16 ch, 1 dc into centre each loop.
If large Bag is required add another 4 rows 20 ch, 1 dc into centre each loop; for medium Bag, which will be found most useful size, proceed as follows:--
25th Row: 8 ch, 1 dc into centre each loop
26th Row: 6 ch, 1 dc into centre each loop
27th Row: 4 ch, 1 dc into centre each loop
28th Row: 5 dc into each loop.
29th Row: 5 dc into dc of first 6 loops, then (for 2st handle) 36 ch, dc back into 1st dc of this row, then work 48 tr into the 36 ch; continue 5 dc into each of next 18 loops, then (for 2nd handle) 36 chain back into dc at end of 6th loop back; 48 tr into the 36 ch; then proceed with 5 dc into remaining 12 loops.
Drawstrings: Crochet 2 Drawstrings (ch) each 24 inches, thread through in opposite directions, attach the 2 loose ends of each drawstring to a brass ring, first crochet dc around the ring to cover.