You just put the variable down (not sure what it is called, however there should be an info section when you press 'n' when highlighting nothing and it should give you a list of things such as g_gravity or g_alienstage3threshold), and in the string/parameters/whateveryoucallthem you list down, with a comma and space inbetween the items you want to disable.
i.e.
"medkit, chaingun, jetpack, level3upg" etc.
I prefer to use a hurt zone, so it warns the player rather than insta-killing em, which makes them want to ragequit and say "gaimap" or something...