Carmina 13:
nam tui Catulli plenus sacculus est aranearum.
Why is the world does Catullus have a little sack full of spiderwebs? Is this a certain expression in latin or something? If so, what does it mean? Is he broke?
Yes, he is broke. sacculus refers to his wallet, it is full of spiderwebs or cobwebs. 
“Little Sack” is also “pocketbook” or “wallet.”
He’s joking about how rich he is.