Example of my .Rprofile

.Rprofile

# If loading in an environment that doesn't respect my RPATH environment
# variable, set it here
sourceDir <- file.path(path.expand("~"), "R", "source")
if (Sys.getenv("RPATH") == "") {
	if (!file.exists(sourceDir)) dir.create(sourceDir)
	Sys.setenv(RPATH=sourceDir)
}

# Load commonly used functions and packages

# enable auto-completion of package names
utils::rc.settings(ipck=TRUE)
# Enable more than 100 packages loaded
 if (getRversion() >= "3.4.0") Sys.setenv("R_MAX_NUM_DLLS"=300)

# Load custom functions from util.R file (see in https://gist.github.com/IdoBar/7f63547158ecdbacf31b54a58af0d1cc)
# if (interactive()){
# if (require(devtools) & curl::has_internet()) devtools::source_gist("7f63547158ecdbacf31b54a58af0d1cc", filename = "util.R")
# if (file.exists(search.path(utilsFileName))) source(search.path(utilsFileName))
# }
# Setup favourite CRAN mirror and a site install library.
# Choose CRAN mirror (1 will use https://cloud.r-project.org/ to Automatically redirect to servers worldwide through ) 
utils::chooseCRANmirror(ind = 1)
# fix "Warning: unable to access index for repository https://www.stats.ox.ac.uk/pub/RWin/src/contrib"
# https://stackoverflow.com/questions/45108484/warning-unable-to-access-index-for-repository-https-www-stats-ox-ac-uk-pub-rw#45112048
options(repos = getOption("repos")["CRAN"])
# options(repos=structure(c(CRAN="https://cloud.r-project.org/")))
# myLib <- "C:/Users/Public/R/MRO-3.3.1/library"
# .libPaths(c(myLib, .libPaths()))

# Function to run when R is started
.First <- function() cat(sprintf("\n\nDefault location to install new packages: '%s' \nCRAN mirror is set to: '%s'. \n\n	Welcome to R!\n\n", 
.libPaths()[1], getOption("repos")["CRAN"]))

An example of an .Rprofile, used to define basic environment and load custom functions from util.R.
Place this file in your home folder (~ in linux or My Documents in windows)

Updated line 5: dir.exist() to file.exists() to be compatible with older R versions (<3.2)

Added an environment variable declaration R_MAX_NUM_DLLS=200 to support larger number of packages to be loaded (for R versions >=3.4)

Updated default CRAN repository

Another update to default CRAN repository (use top of list rather than hard-coded address).
In addition, remove sourcing of util.R, it is better practice to source it from Gist only in scripts as needed for portability.

Remove CRANExtra repository which causes warning (and leads to errors in the installation of some packages).
See this SO thread.