Medicine is a helpful tool. To use it, press the start button while in an area. When you use it, you'll regain all your lost life points.

Area 4 is underground, and without flare bombs, you won't be able to see very well. When you enter Area 4 with these equipped, press start to use them. (You can still beat Area 4 without these, but it's much harder.)

Used as an add-on to your normal gun, this item allows you to shoot much faster. It really isn't all that great, because you'll usually have much better items to choose from, or a better gun.

There are two neutral zones where you can only enter with the permit. Areas 14 and 18. Take the permit to allow access to those areas.

When you're wearing the iron boots, you will be able to kick people and kill them when you swing into them. By the time you get them, there are much better items to use, so they are pretty much useless.