I'll second @jrelewi - I thought package development would be this massive undertaking, and it can be, but making a basic package that is really just for you doesn't have to be. I have a small package that I named after myself on GitHub. I have no intention of ever submitting it to CRAN, but I use to to store a few "general" functions that I find useful across many projects or tasks.
I do have continuous integration and unit testing set-up on it, but it is not very developed and a simple package that is just for you likely does not need that at the outset.
In addition to what @jrlewi recommends, here are a couple of other resources: