You must not be setting yourself as a normal player correctly. Basically, a player without the admin flag "o" (or custom1) the player, with your settings, would only be able to buy 1 flashbang, 1 hegrenade, and 1 smokegrenade.
If you have root access, then you will not be limited and you can buy the max (VIP) ammount.
To change the default admin flag I set for this plugin (which I see I forgot to mention in the OP), just set "grenadepack2_vip" to whatever flag you want in the admin_overrides.cfg file
The below example would change the flag needed to be VIP for this plugin from "o" to "c" (for admin flag kick)