Board Game Arena

Collector (C104):

This card is an action space for you only. When you use it for the 1st/2nd/3rd/4th time, you get 1 begging marker and 6/7/8/9 different good of your choice.

What does it mean by "good"? Is this limited to building materials (wood/clay/stone/reed) or does it include produce (wheat/veg) and livestock (sheep/pig/cow)? Can I choose?

It does indeed include building materials, crops and animals. You can choose which one you get but they must all be different.

Wow, even with a cost of -3VP per use that seems powerful!

"Goods" is a specific term defined in the revised rulebook/appendix. Overall this revised edition of Agricola has pretty precise definitions for things fortunately.

The above answer is correct, with the addition that food is also considered a good. Therefore the full list of things you can pick with Collector includes:
Food
Wood
Clay
Reed
Stone
Sheep
Boar
Cow
Grain
Vegetable

Thanks for the precise answer.