Ask them for the trub (rhymes with rube in the US and with rub in the UK). That's the layer of sediment at the bottom of the fermenter when brewing finishes.

Depending on the process they use, they may also have other waste products from various stages of the brewing process.

The main thing that microbreweries have is spent grain. It is a very potent green in the compost pile. I've been getting a few 5 gallon buckets per week from the local brewery. I think I like using the grain better as a mulch. It mixes very well with my primary mulch material which is straw.

either would be fine
just be aware if you get some spent grains to mix it in with browns very well or spread it very thinly as a mulch
because it will stink as bad as can be imagined if it is left in a bucket or in thick clumps.
Believe me
it will make you gag in a day or two if you don't
It is an excellent material to use with these precautions
I use it when I get it
good luck

As I home brewer, I have to agree about the stench of funky spent grains. Don't let this stuff fester!

With the high protein content of spent grain I would be surprised if they are discarding it, a lot of it goes to cattle feed. But if they're a small local brewery they may not have established that market connection, or maybe you can snag a few buckets anyway since you have an employee connection.

Tip one back for us too!

if they use leaf hops, that would be good. any spent yeast may be good as well, but I'd imagine you'd have to use it in small quantities.

ooo, don't forget the beer it'self! there is usually a bit of wort (brewed 'beer' before the yeast is added) or green beer that is discarded during the process.