Gift Box
This box made from two bills. The bills/box can be the gift itself, but it is also just about the right size for a ring box. (Perhaps a dollar-bill ring?)
Get yourself two fairly new, crisp bills. Older "soggier" bills are much harder to work with. For this design to work, the folds should be very precise, and perpendicular to the edges of the bill if the resulting is to be retangular.
Lay
the bill on a flat surface, face up. Fold the bill in thirds lengthwise
as shown. Gently unfold these folds, you will reuse them later. I will refer to
these as the third folds.

Fold the note top-to-bottom just to the right of the portrait, then unfold. Repeat just to the left of the portrait. I will refer to these as the portrait folds. Note that the third folds the oppose (are perpendicular to) the portrait folds.
Starting at the top left corner (as illustrated), close the top third
fold to about 90 degrees. Lift the right edge of the bill to the right of the
right portrait fold up while holding the top third fold in place,
allowing the third fold to close completely to the right of this corner.
Inside
this corner will be a remaining portion that you will crease along the natural
45 degree line to complete the corner.
Complete the previous step for the other three corners. Now you will have two
"tabs" sticking up on the left and right sides.
For
each tab, pull it inside the box, folding so that the natural edge of the box is
pulled slightly over inside the fold. (Look carefully at the
bottom left of the picture.)
Do this evenly for both tabs.
For the two other sides, evenly fold over the edge of the bill.
You should now have an open box.
If you make another piece just like the first, but slightly larger, you would have a lid similar to that found on most shoe boxes. To adjust the instructions above, you would fold so that the inner rectangle (bounded by the third and portrait folds) is slightly larger.
I do not like the way that looks, so I close the box another way as illustrated below. Try both - choose whichever you prefer.
Fold
the second bill lengthwise so that the width matches the widest portion of the
open box you just made. I will refer to this bill as the cover, and the
previous piece made as the open box in the following steps.
You need two folds as shown to be able to follow the last step (see below).
For general appearance, it is nice if these are nearly symetrical as shown.
These will be called the width folds.
Holding one end of the cover across the bottom of the open box, find the point
which matches the corner of the open box and fold at that point.
After folding, open the fold to 90 degress, hold the cover back in place, and
find the point for the next corner of the open box as the cover wraps around.
Repeat this process until the cover wraps over itself (four folds).
These will be called the wrapping folds.
There
is now one very long side to the cover. Fold back the long side so that is just
a bit shorter than the first side.
I will call this the end cover fold.
In this illustration, the end cover fold is at the left edge of the picture. I have also (gently) completely unfolded the cover, refolded the end cover fold, the width folds, then the wrapping folds in that order. (This unfolding/refolding is optional, but makes the cover look nicer.)
In either case, the end cover fold puts the remainder of the long side inside
the wrapping folds. Refold the wrapping folds holding the long side in place to
crease it at the correct points.
Open
up the width folds slightly on the open end, and insert the last side under the
width folds. (Normally I do this with the open box already inside, but for
clarity, the picture shows this without the open box.
Slide
the open box inside the cover before closing the cover tightly, or close the
cover with the open box already inside. In either case you are done.
Of
course if the gift box is for something special, a little ribbon adds a nice
touch. (I used ordinary curling ribbon, cut in thirds lengthwise for this
picture.)