Thanks for the comments! Sounds like we need to adjust our code, as the health packs should be dropping from enemies more frequently. They should also have a higher chance of dropping, instead of a gun, the lower the player's health is.
They aren't in the demo, but we have "health recharge stations" that fill the players entire health and shield. They will be found at half way points in the level and will be impossible to miss based on the level design.
Noted on the grenades! We've got a few versions we're playing around with. The current ones mimic that of the Metal Slug grenades.