A "sit-upon" is described by the 1940 Girl Scout Handbook as follows: "It is not wise to sit or lie on damp ground, so put your sweater or "sit-upon" under you. A sit-upon is a piece of waterproof material about eighteen inches square that a wise hiker carries along in a compact roll to use while resting, eating, or sitting around the campfire."
I decided to knit myself one after a long, cold day of rock climbing last January, when I spent many hours sitting on freezing rocks. My sit-upon is knit in a ribbed cable with a rugged worsted wool, which yields a dense, reversible, and doubly-thick fabric. An oilcloth backing makes it waterproof.
Here is the pattern for you, just in time for autumnal hikes, picnics, and football games. I'll also be putting this on Ravelry as a free download.
Small (17" wide x 15" tall), Medium (20.25" x 17"), Large (23.5" x 19")
note: You can knit it to any size by casting on more stitches (repeats of 8 stitches) and knitting more rows (repeats of 8 rows). I started with such a small size to make it fit in my climbing pack.
* Yarn: S [M,L] takes 2 [2,3] skeins of Bartlett Yarns Fisherman 2-ply (100% wool; 210 yds/4 oz) in the color "Bark"
* Knitting Needles: US 7/4.5mm circular needle, at least 24" long
* Notions: cable needle, tapestry needle
* Waterproof backing (optional): oilcloth or vinyl fabric. I made holes along the edge of the oilcloth with a small (3 mm) holepunch and crocheted it to the knitted sit-upon with a F-5/3.75 mm hook.
16 st/24 rows = 4" in stockinette stitch
K = knit
P = purl
C8B = "cable 8 back": Slip next 4 stitches to cable needle and hold to back of work; [K1,P1] twice from the left needle, then [K1,P1] twice from the cable needle
* Cast on: 128 [160, 184] stitches
* Bottom edge: knit in [K1, P1] ribbing for 5 rows
* Main fabric: knit a cable row by knitting across in C8B, then knit seven rows of [K1, P1] ribbing. Repeat these 8 rows until piece measures 14" [16", 18"] tall
* Top edge: work one more cable row, then [K1, P1] ribbing for 5 rows
* Bind off
Weave in ends using the tapestry needle.
If you want to add an oilcloth backing, cut a piece of oilcloth to fit the size of the knit fabric. Punch holes approximately every quarter inch (6 mm) along the four edges of the oilcloth. Attach the backing to the knit fabric with single crochet or simple sewing stitches (blanket or whip stitch). Alternatively, you could attach it with velcro or by machine- or hand-sewing.