You can put your csv files in the data directory or in inst/extdata. See the Writing R Extensions manual - Section 1.1.5 Data in packages manual - Section 1.1.5 Data in packages.
To import the data you can use, e.g.,
R> data("achieve", package="flexclust") or
R> read.table(system.file("data/achieve.txt", package = "flexclust"))