A perennial favourite, I tend to make party bags for the kids out of C5 envelopes. This year was no exception.
Cameron had a bowling birthday party, and although I chose to use clip-art and fonts from the printer instead of stamping, I have kept to my normal envelope-bags.
I learned the envelope bag trick from a Stampin Up demonstrator about ten or so years ago. I've been using it since the kids started having birthday parties! The basic envelope-to-bag technique goes like this:
Seal the envelope.
Score down the two long sides and across one short side, all scores the same distance from the edge of the envelope. You can vary this measurement all you like as long as it's the same on all three sides.
Cut the other short side off, leaving an open top.
Reinforce scores by folding in both directions crisply. It also helps to score a diagonal line connecting the intersection of the score lines and the corner of the envelope.
Once these steps are done, you just pop it out into a bag shape, fold the corners under and glue them down on the bottom of the bag, and decide if you want to fold over the top and staple it or add ribbon handles, in which case it helps to double up the top margin of the bag and then punch holes.
If you're decorating the bag, especially if you're stamping, you'll want to do that while the envelope is still flat. Score it first, then decorate, then move on to the next steps.
What I did was use two Distress Stains to add sketchy stripes to the bottom of the bag, all around the front, back and sides. A lot of this got covered up, so it doesn't have to be perfect. I added the main motif which I ran off on the printer, using the same font and graphic as his invitations. I scribbled around the edge of the motif with one of the distress stains and used the other to colour in the flap where I would fold over the bag. After I filled the bags, I folded the coloured tops over and stapled once in the middle.
Envelopes like these are 25 for a pound, but you could go for higher quality if you wanted them to be a bit more posh, like for a wedding or baby shower. In the past, I have used brown envelopes and stuck a white punched border on the top flap for contrast. The possibilities are endless!