> I've finished the boosters, the conduits, the maintence thingy...
> and been on the "radio" trip.
> I found the cat, gave the boy a better weapon, solved the King's Dilemma, shot the bear thing and now I have no clue what to do next.
> -how can I get the Spiffy Cola in that vending machine?
> -how can I get into the sandstone caverns?

Pay careful attention to what happens when you jump from the mine cart along the central railway (just past the second barrier). You can still hear the mine cart rumbling around somewhere...

> -where can I get more evidence for Johnson?
> -how can I get into Kepler's office and stay alive?

There are two ways to get in or out of the office, and you've had to use them both. See if you can get in through a back door.

> -where is the silver key?
> (BTW, I stupidly gave back Fisher's card... hope it's not important)
>

All of your other questions should be resolved in time; focus on these two main approaches for now.

Oh, and it's not a bear. :-)