Our invites were designed in Inkscape, an open-source vector graphics editor, using travel icons from the Open Clipart Library. Polka dot patterns came from junelily studio.
Invites and envelopes were roughly 4 1/8" x 9 1/2", and were printed on 8.5" by 11" cover-weight paper, fitting two sheets per page which were then cut to size using a paper trimmer. It's a little hard to tell from the photos, but the invitations are layered, with upper layers being about 2cm or 3/4" shorter than the layer underneath. The layers were arranged so that the watermark appears to be a contiguous image, with the upper layers hiding text underneath.
Printing was done on a laser printer at the local copymat, but you could probably get great results from a home or office color laser printer.
Invitations were finished using a corner rounder punch. The middle sheet had a tear-off RSVP card that was self-addressed and stamped, which were made using a handheld perforator. Sheets were then assembled and stapled together. [links are examples]
Stamps were actual vintage USPS stamps - we used stamps common enough that they were priced at or around face value of the stamp.
Fonts were found on Font Diner (Fontdinerdotcom Sparkly) and dafont.com (Honeyscript, Marketing Script, Traveling Typewriter). It also uses Futura, which is a commercial typeface included in Mac OS X.
I've attached templates to this photo 'ible for each sheet of the invite - sheet 1 is the invitation card, sheet 2 is a detachable RSVP card, and sheet 3 is for directions and additional information. There are also faint guidelines for cutting upper layer sheets to length. Colors can be customized for each object in the template.
The watermark is on the lower layer of the vector graphic file - for these templates I've included a star shape as a place marker. The watermark should be in the same place on each sheet in order for it to seem like an airline printout. If you are making additional sheets I would suggest putting all watermarks in a separate layer, and then copying that layer between files so that they stay in the same place.
Our watermark and logo were taken from a scan of a rubber stamp that was made by This is Just to Say in Stockholm.
The programs were 8 sheets front-to-back, and printed on both sides of a 8.5"x11" sheet of cover-weight paper.
Each program included a set of vintage pinback kiddie wings (purchased on ebay) - holes were punched in the cover to fit the pin. These were a big hit with kids and adults alike.
Programs were bound using ribbons and a 1/8" hole punch; corners were rounded using a corner rounder punch.
Our luggage tag escort cards were designed in Inkscape, and were printed on manilla shipping tags that we got at an office supply store. The tags were printed using Printer Gocco but any sort of screen printer or a rubber stamp would work great.
We displayed the escort cards in a vintage suitcase near the entrance to the venue, and matching tags were used as place cards at each guest's seat.
Lastly, these photos were taken by the talented Ting Aurelio of www.tingphotodesign.com.