First of all, I use this clip on, clip off rear rack on all my bike touring (i was able to buy just the rack). I put my tent, pad and sleeping bag and puffy jacket into a 20l dry bag under the rack and clip the buckle onto the rack near the seatpost. Then I put my clothes, food and stove into this 20l yellow bag on top of the rack (it usually only has 10l of gear, but is big enough for when I stock up)
Then I use a strap that goes from the back of the lower bag, cross it over the top bag, and clip it on the saddle rails.
I have toured for a total of 3 months with this setup without any problems.
The advantages are :
- it doesn't stick out into the wind, and actually improves the trailing edge of the aerodynamics
- it can be taken off the bike and carried with one hand to camp
- it makes it easier to pack the bike up small for train and plane travel (racks are a pain for that)
As for a cheap, light rack, I've used this Pletscher which can be stripped of it's spring and dremelled to get down to under 300g. IT works on front or rear
I can only encourage you to go as light as possible on gear, I spent 6 weeks crossing Vietnam from N > S with a 9-liter handlebar bag and under 6 lbs (2.5kg), it was liberating.