Meaning of "boosting cat food from someone"
Solution 1:
As cornbread ninja says, boost is to 'steal'. Cat food is, according to Urban Dictionary option 6 is 'crack cocaine'.
So, the overall meaning is:
No, man. I didn't steal any crack from you.
Solution 2:
To boost something means to steal it.
Slang . to engage in stealing, especially shoplifting.