There’s a double meaning in that.
There is the sense that they will step in and take care of the king’s needs. And there is also the sense that they will provide for themselves. And that they will deliver to themselves what THEY need. All things are true at once.
That is, they will be both self-serving and serve the king, simultaneously. I’m not sure which Guildenstern intends to say. (My money’s on serving the king – but he gives away his true motives simultaneously.)
The Hamlet Project 