The phrase "few kernels" means there are only a small number of something. It implies that there is not a lot or not enough of whatever is being referred to. Full definition
For just about any other car that breaches 200 mph, picking up additional speed is like popping the last few kernels in the popcorn bag. (automobilemag.com)
heat up oil at medium temp, throw in a few kernels & wait for them to pop. (morestomach.com)
Disclaimer: It's messy to eat, and a few kernels will topple out, but that's perfectly fine. (tastingtable.com)