Array modifier seems to add more objects into this model which may sometimes be unwanted. A Particle system applied to the coin seems to make a bit more sense if we don't want to unnecessarily add objects to this system. So between particles vs. array, which one should be used?
Also to fix the issue of coins falling straight through the box, add a solidify modifier to the box. The simple paper thin box is not "thick" enough to hold the coins, A solidify modifier with thickness of 0.15 was enough for me to fix the issue of coins falling through the chest.
knightwolf the problem with a Particle System is that you will get intersecting coins and coins floating in the air.
That makes sense, I thought there might be an option to have rigid body physics applied to particle system.
@theluthier there is an addon, the molecular script, which has been updated for 2.80 by scorpion81.
It combines Particles with Rigid body Physics and has many possibilities, but as far as I know, it only works on spherical particles...
The addon can be found here: https://github.com/scorpion81/Blender-Molecular-Script/releases
And Moby Motion has done some nice tutorials on YT on how to use the addon (for 2.7...).
@theluthier it has been out of development for about 6 years, but now Martin Felke has taken over, so it's in good hands!