I have a missing resonator cap and sometimes the car shuts off when I hit the gas

You can try but I doubt it will hold. If you take a look at the picture of what appears you are getting, it has a double seal. This is critical to ensure it remains sealed. Plug it has a lip formed into the body of it to ensure it stays seated properly. Granted this is for a Chevrolet van so yours may be different because I did not find the product for a Toyota van.

If you cover it, just make sure it is with something that cannot get sucked into the engine.

If you can wait until it arrives, that may be best if you cannot make sure it is sturdy. There are a number of videos online showing tricks for this. I will leave that for you to search because I would not recommend what they are doing but it did look like it worked at least for the length of the video.