"Twitch pennies" is a generalized term for Bits, the digital currency associated with the streaming platform Twitch. One Bit is equal to $0.01 USD and they can be redeemed with qualifying Twitch channels in order to "cheer" in their chat box and earn increasingly more ornate supporter badges for your profile. Bits can be acquired by watching advertisements or bought outright at approximately 140% of their actual value.
By meeting the qualifications for Twitch's "Affiliate" system, Gatorbox is one of the many channels where Bits can be redeemed. The channel met these qualifications shortly before the August 2017 production hiatus caused by Hurricane Harvey, and in that time Draco took a liking to calling them "Twitch pennies" because that's what they were by literal definition. Usage of the term slowly fell out of favor during the hiatus over fears of repercussions for insulting the platform. However, as of 2018 the term is not only still in use but Draco is actively trying to use it more often in order to get the most use out of the Bit Sign he built to further add to the gimmick.