Reading all scripts and data files from multiple folders

for (f in list.files(pattern="*.R")) {
    source(f)
}
for (f in list.files(pattern="*.rda")) {
    load(f)
}

Since .rda requires load and .R requires source, I would do something like this:

file.sources = list.files(pattern="*.R")
data.sources = list.files(pattern="*.rda")
sapply(data.sources,load,.GlobalEnv)
sapply(file.sources,source,.GlobalEnv)

Update for reading from multiple folders at once

file.sources = list.files(c("C:/folder1", "C:/folder2"), 
                          pattern="*.R$", full.names=TRUE, 
                          ignore.case=TRUE)
data.sources = list.files(c("C:/folder1", "C:/folder2"),
                          pattern="*.rda$", full.names=TRUE, 
                          ignore.case=TRUE)
sapply(data.sources,load,.GlobalEnv)
sapply(file.sources,source,.GlobalEnv)

Notice also the use of $ at the end of the search pattern, to make sure it matches only, say, a .R at the end of a line, and the use of ignore.case in case some of the files are named, say, script.r.