I just ordered a futaba 6exa radio which comes with 4 servos.
I am gonna order a red rascal 40 size arf and a OS.46 LA engine from Tower website.

I am also gonna order the following parts:

2 props, fuel tubing, glow plug heater, fuelpump( manual ), Servo Extension: Two, 24" for aileron servos, Y Harness: One for aileron servos, 1 S3004 standard size ball bearing servo and some latex foam rubber.

Do I need a Muffler?

Is there any thing else I am missing before I order? Should I order a few from tower and buy rest in a local hobby store?

thanks.

747, A muffler will come with the engine and you'll need a spinner. Oh and fuel of course.

I don't believe the OS .46LA engine comes with a glow plug. Get a couple of #8 OS plugs. You also need a glow plug wrench. Might as well get the kind that looks like your car's star wrench for the lug nuts. This 4-way wrench will tighten your glow plug as well as the prop.
You also need something to start the engine. You can get a chicken stick, or better yet, get a 12 volt electric starter and starter battery. You'll need a charger for the 12 volt battery.