With this particular example I think you can just use the merge function. As a standard its arguments all.x and all.y are set to TRUE, so it automatically creates all combinations since the dataframes do not have any variables or values in common.
df <-data.frame(a=letters[1:10] )
df1<-data.frame(one=1:10)
dfcomb <- merge(df,df1)
dim(dfcomb)
[1] 100 2 #gives 100 rows and 2 columns
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