library(raster)

# create raster data from scratch
# create empty raster
y1<-raster(ncol = 3, nrow = 3)

values(y1)<-1:9

projection(y1)<-CRS("+init=epsg:4326")

# create and diversify the rasters
y2<-y1+10
y3<-y1+20
y4<-y1+30

# make list of rasters
y.list<-list(y1, y2,y3,y4)

# plot all rasters at once
par(mfrow = c(2,2))

for(i in 1:length(y.list)) {
  plot(y.list[[i]])
}

y1  y2  y3  y4
pixel1   1   10  20  30
pixel2
...
pixel9   9   19  29  39