Bands(also spelled bandz) is slang for money/cash/etc. This slang comes from the fact that some people and banks also use bands to hold large amount of money together. Bands is similar to the word guap in that it refers to rather a large amount of money, however, people often use it for any amount of money. Bands is also an actual english word which means "a flat, thin strip or loop of material put around something, typically to hold it together or to decorate it".
This slang is very popular in rap music in which musicians often boast of their large amount of money, in L'A Capone's 'Some More' song, he says "We gon' hit the mall and we gon' hit the stores Then we gon' blow some bands yeah then we go get some more".