So last night I saw this instructable but knew that I didn't have time to make that for Fourth of July. I did have some cardboard lying around though, which became the basis for this (hopefully) two-sided lawn game that was made in less than 30 minutes.
Measuring Tape/Ruler/Straight Edge
Glue gun (could substitute white glue or even packing tape)
Decorative tape (optional)
Disposable bowls (optional)
Step 1: Cut Your Cardboard
I used the flaps off a large box with the long end measuring 27in on all three pieces. However, no specific dimensions are needed. I suggest that the width/length ratio of your biggest piece be around 40 to 60%. Here, width to length is 59%. Traditional cornhole uses a 50% ratio (24in by 48 in).
Since the long pieces will go on the width section of the big piece, score the outside sections so that the can fold in. In this case, measure 5.5in away from the outside on each side since (27-16)/2. Do this for both long sections.
In addition, use your ruler, compass, measuring tape, straight edge, etc to mark off a triangle section and cut off each end, approximately 1-2 in from the score line. The game will rest on the 1-2 in section.
Step 2: Glue the Backboard/Stand Onto the Game Board
Apply glue to the visible flutes on one of the small backboard pieces (make sure the flat side is on bottom, not the cut triangular side). Press hard onto the short end of your game board, trying to obtain as close to a right angle as possible.
Once the center part is glued, apply glue to the flaps and fold them into place, one at a time.
Once this side has glued, flip it over and repeat with the other long piece on the same edge of the game board.
The board can not be flipped over and rested on either side.
Step 3: Tic Tac Toe Game
Now it's time to decorate!
The first game we decided on was bean bag tic-tac-toe. Like regular tic-tac-toe, you must complete a row/column/diagonal of three to win. However, in this game you must throw the bean bags from several feet away, increasing difficulty.
To create this game, the board must be separated into 9 equal sections. First, measure across the bottom marking 1/3 width from each side. 5.33 inches here. Next, measure up from these markings 1/3 length, 8.6 here and then another 1/3 from that mark.
Using a straight edge, connect the marks, forming two horizontal lines and two vertical.
At this point, you could stop or you could add additional decoration. Using this "duct" tape, I covered the lines and the backboard of the games to give it a more festive look.
Step 4: In Progress: Bean Bag Toss Game
For the other side, I wanted to a classic bean bag toss with different "holes" that were worth different amounts of points.
Clearly, holes would ruin the functionality of the piece. So instead, disposable bowls could be glued on to the board to catch the bean bags.
Unfortunately, it was at this point that I discovered I had no disposable bowls in the house and the few cups I had were too small for the bean bags.
Will update with finished board hopefully after a trip to the store!
Also considering drawing on a bullseye pattern instead to play bean bag king-of-the-hill (players try to knock other players' bean bags off the board while keeping theirs close to the inner rings--somewhat similar to curling) if there's no time to complete the other.
Step 5: Weather-Proofing Notes
The cardboard here is pretty strong and durable (off of a furniture box), however, to make it stronger and less susceptible to weather, the whole cardboard surface can be covered with clear packing tape.
Based off other instructables, enough tape seems to make the cardboard waterproof.