[Update: Tom Silverstein has since reported that the Packers currently have around $13 million in salary cap space, not the $5 million he reported on Monday. The discrepancy appears to be due to the team accounting for their draft class and a small amount of cushion for the regular season.]
The Green Bay Packers like to go into the regular season with a handful of salary cap space in order to maintain some flexibility for the season. Typically something around $8 million is in place to cover any unexpected transactions, cover players who go on injured reserve, or land the occasional in-season contract extension.