I have found that the best thing to purchase is a certificate; as it lasts forever, increases crop production, and allows more types of crops to be planted. The only downside is the cost.
Bye the way, the first gun is a model 2002 S.T.E.N., and it shouldnt be that accurate.
The grenade launcher is a model 2001 R.E.V. volver.
The rocket is made up, just like the shotgun.