I use this on my on my deChromebook — a C720 with Chrome removed and Linux installed. Some of my Internet access is via Internet-On-The-Go, and, knowing how much bandwidth I'm using is usefull. I can use the network monitor part of the network panel plugin, but it's just as easy to use a little script.

Here's the script:

#!/bin/bash

traf=$(ifconfig wlan0 | grep RX\ byte)
echo $traf
sleep 5
wmctrl -r wlan0-stats -t 1 
while :
do
  clear
  traf=$(ifconfig wlan0 | grep RX\ byte)
  echo $traf
sleep 20
clear
sleep 2
done

I use a panel launcher on my desktop to start the script and put it on the second desktop (numbered 1 in Xfce.) This could be easily converted to a menu launcher.

And the Launcher content (Watch the long non-wrapping line):

Name: ifconfig
Comment:
Command: xterm -fa 'Monospace' -fs 14 -title wlan0-stats -bg yellow -geometry 60x2+500+1000 -e "/usr/local/bin/t-ifc"
Working Directory:
Icon: (as desired)
Options unchecked

Here's what they do.

The script t-ifc:

traf= ; gets the RX/TX line for wlan0
  in the variable, leading spaces are stripped
echo ; displays it
sleep 5 ; leaves it in launch workspace for 5 seconds
wmctrl ; moves named window to second desktop (1)
while ; starts endless loop to update window
do ;
clear ; clears window
traf= ; gets RX/TX in loop
echo ; puts it on screen
sleep 20 ; leaves it there for 20 seconds
clear ; clears window
sleep 2 ; leaves empty for 2 seconds
done ; completes loop - do it again

The launcher:

Name: ; call it something
Comment: ; I don't use.
  If filled will be included in tool-tip
Command: ; Open xterm and run the script
  -fa/fs ; make it readable for old person
  -title ; sets window title for wnctrl to use in the move
  -bg ; set background color for xterm window
  -geometry ; set size and position of window
  -e ; command to execute
Working Directory: ; I don't set
Icon: ; (as desired, I usually make my own)
Options unchecked