I built alot of these types of kits and mostly they don't come with boxes to protect the circuits. Alot of times they also don't come with parts that accommodate them for being in nice boxes either. So you'll have to buy some extra parts.
For this project I bought the Traffic Lights Kit and the XXL Green LED Blinker kit from Electronic Goldmine and put them in one box with one battery and a switch to switch between kits. You can also buy them from Electronic Kits By Chaney Electronics for a little bit less, but I would buy them from Electronic Goldmine even though they are a little more, they have great deals and sales from time to time.
Step 1: Plan Your Enclosure
Decide what box to use. I used this one from Radio Shack.
Lay the parts onto the box where to plan on putting them.
Step 2: Measure the Hole Placement
Then tape a piece of paper to it and measure the placements of your parts and mark the places with a marker.
Step 3: Mix All the Parts From Both the Kits Together (Experts Only)
This step is going to require precision sorting skills when it come to time to place the pieces on the board.
But it won't be so hard as long as you know how to tell the difference between resistors color codes.
Step 4: Drill the Holes
Now that you have marked where the hold are going, drill them out.
Then place your components in the holes to make sure they fit.
Step 5: Paint the Box Gold
If you want yours to look like mine, before you finish everything paint the box gold.
Step 6: Solder on the Parts
At this point only solder on the parts that don't need to be externally mounted.
That means solder in the capacitors, resistors, IC's, and transistors
Step 7: Connect the Two Kits
To do this I connected the positive of the battery connector to the middle of a SPDT switch and on other side to the middle of the other SPDT switch.
Then I connected each side of the other SPDT switch to each of the kits respectively.
Then I connected the negative of the battery connector to the negative of one kit along with an additional wire in the same hole to connect to the other kits negative.
This way you turn on one switch to supply power and the other switches between kits.
Step 8: Put It in the Box
Now put the kits in the box and screw in the switches.
They might move around while in the box during operation so I used some thick double sided sticky tape to hold the two circuit board in place inside the box.
Also Glue the LEDs onto the box.
Step 9: Wire It Up
Now solder on the wires to connect the external parts.
I used a plastic zip tie to hold the wires together.
See it in action: