I’ll hazard a top-of-the-head response to reflect mind share, after mentioning two essential find-the-tool helpers. CRAN Taskviews give a curated view of leading packages by domain. rseek.org is an R-tuned Google front end.
The fpp3 suite of time series tools (successor to forecast())
lubridate for simple date time parsing
sf for gis
rms, the regression companion to Hmisc
gt for table formatting when I’m not using xtable
RMariaDB for SQL
nortest for Anderson-Darling and other normality tests
here for path reference sanity
RGraphviz to make simple graph objects
Rcpp, reticulate and RJulia
My house rules: never use a data frame where an array will do; never use a tibble, tidy NSE, purrr, and remember the magic of linear algebra