dont get last then
there are discussion about all that already.
powerup discard, balancing powerups depending on your position, being able to switch the shields position between front and back (to block mines and stuff) and im pretty sure its easy to implement that the RNG wont give you 2 shields.
so far i never had 2 shields at the same time, but rockets and machineguns.
at this point we dont know how powerfull the shield really is.
we will see once all weapons are in the game and maybe having a shield and 2 weapons ready will prove to be too powerfull, we'll see.