It seems like the word extreme is going unheeded in this thread, so here are some proper measures to REALLY get the weight down:
My first tip would be to mount your battery high, as you move it away from the earths center of mass, it gets lighter by the increase in distance squared, equaling huge savings.
Placing magnets along the top of your chassis can also help you hang, as the attraction between the magnets and your chassis creates a net force upwards, improving your hang. Make sure you test this with a roof over your head, I nearly lost my first robot when I put on one too many and it started flying into the air.
Sand the back of your registration plates. This reduces the weight you need to invest in non-functional parts, but be careful, sanding them back too much can make your plates prone to breaking, and only noobs do that.
Paint your robot white, this reflects any extra unwanted photons that could become stuck to it saving you hundreds, if not quadrillions of yoctograms.
Fill any empty spaces on your bot with polystyrene, as it is a very light material.
Fill your pneumatics with helium. Although it was Q+A that you must use air the vex staff failed to specify from what planet, so the atmosphere of Jupiter should do nicely.
Avoiding side plates can save you the weight of 2 sheets of cardboard, 2 sheets of paper, and the ink on them. If your sponsors don’t understand the need for intense deweightifying at least use a laser printer, as the toner is significantly lighter than ink.
My final set of tricks are related to manipulating the aerodynamics of your bot, a pair of wings can really take the weight off at speed, and they were often used in gateway to give some bots a bit of an extra jump at the 30” goal.
Any spare motors should be put to rotating lexan helicopter blades to increase your up force.
If you add up the weight savings here, your robot should be able to go well into negative weight. This changes the nature of your materials to anti-matter, which means if a game is going poorly you should be able to ram into your opposition and completely remove them from existence, this will also obliterate your bot, so I would recommend perhaps saving that tactic for finals.
Best of luck in your weight saving measures