Ok, so I know fanny packs are probably considered uncool...but I'm making it my mission to bring em back. Here's my version. I've been playing around with the design a bit. I needed something that I can wear when I shake my booty on the dance floor. Here's what I came up with:
For the belt closure I used carabeeners (um, I think that's what you call them. Not sure about the spelling either).
And the carabeeners are attached using velcro so that the size of the belt can be adjusted.

I tested it out yesterday on my walk to the park. It held up really well! I was able to fit in my cellphone, a slim wallet and my tiny digital camera. And the carabeeners served a dual purpose cause I stuck my keys on there, too. Now my hands will be free to flail around when I'm rockin out to some good tunes on the dance floor.

TUTORIAL!!!
Ok, here it goes. First off, I hope this makes sense. I also have a phobia of numbers and math so if you find some errors then please let me know. This is the easiest method that I've come up with. If anybody has any questions please feel free to ask. I'll do my best to help! Or if anyone has suggestions to improve it than that's cool, too! These measurements are based on the first hipslinger I made and the one for the tute. You can always change it all around to suit your needs!
Materials you'll need:

Measurements:
Bag (Outer X2 and lining X2): 25cm in width. 19cm in height
Belt: 116cm X 15cm
Velcro pieces: 25mm X 20cm
Flap: 19cm X 7 cm
Caribeeners: 5.5 cm
STEP 1: BELT
a. I used 116cm x 15 cm of fabric to make this belt.
b.I folded the sides in (lengthwise) 1.5cm. Ironed. Then folded it in half. The finished belt is about 5cm in height. (I realize there are easier ways to do this. I just ran out of fabric and was conserving. The Jordy Bag Tute
http://www.craftster.org/forum/index.php?topic=32204.0 shows a great way to make straps. **You may also wish to make the belt thinner or thicker. Just remember that if you use caribeeners to make sure the belt fits into them!

You can also make it longer or shorter depending on your measurements. My lower waist is 33-35 inches depending on the pair of jeans I wear. And this belt is more than long enough. This belt is pretty long though and can be adjusted easily. Again, it's up to you!**
c. Next cut the velcro pieces in half and place as shown in the picture to both ends of the belt.
STEP 2: BAG
(outer and inner pieces) are all 25cm across the top. And from the center of that measurement 19cm up and down. In order to get the curved shape of the bag I drew it free hand on one side then folded it in half and cut along that line. You could also use a bowl and trace it. Sorry I don't have pictures of this, but you can get an idea of what I mean in
Step 3
a. You'll want to make an opening or what I'm gonna call "The Mouth" of the bag. From the top center of ONE piece of the outer material measure down 5cm. Mark it. Now draw a line 14cm in length. At the ends of the line draw inverted arrows 1/2cm. (**The bigger you make these lines the bigger your "mouth" will be. So proceed with caution.**)
b. Cut along those lines. Fold the pieces back to "open" the "mouth" and iron. Sew around the edges. Now repeat with ONE piece of lining fabric.
c. Now take your outer pieces (one with mouth and one without) and sew them together along the curved edge. Right sides facing. DO NOT sew along the top. Repeat this for the lining.
d. Take the outer bag you just made and turn it right side out. Take the lining you just made (wrong side out) and place it inside the outer bag. Match up the mouths for a nice lip-lock. Pin and Sew.
STEP 3: THE FLAP *Note: these are measurements based on the size of the mouth made above. If yours ended up being a big bigger or smaller than adjust your measurements to fit.
a. draw a rectangle 19cm X 7cm. Now using a cd trace and create a curved line on ONE SIDE of the rectangle.
b. Fold in half and cut. This is so that both sides are even. Repeat using the lining fabric. Place the one you just made on top of the lining fabric and trace/cut.
c. Place those two pieces together (right sides facing each other) and sew along the curved edge. DO NOT sew the top.
d. Now turn it right side out and fold in along the top. Iron but DO NOT sew.
e. Now take the flap you just made and pin it slightly above the "Mouth" and sew across the top. *make sure you don't pin the back of the bag with it. You only want to sew it onto the front of the bag.*
STEP 4: CLOSING TIME (almost there!)
a. Now you're going to close up the top of your bag. Remember how you closed up the top of that flap? Do the same to the top of the bag. Iron but DO NOT sew.
b. Now pin that bag to the belt. Make sure that the velcro side of the belt is facing down towards the floor. Sew across the top.
And hooray, you're finished! Time to go out and shake that thang on the dance floor, on your bike, in tourist traps...wherever your hearts desire!

Oh, and ps. If your still fannypack-phobic you can wear it across your back if you make the belt long enough!