Buggy--20+ gallons. Every single piece, including the chassis, except the nuts, bolts, and screws. But mine started as a RTR two years ago. Probably a gallons' worth of diff fluid and shock oil. Bodies and tires.
Truggy--5 gallons roughly. Clutch shoes twice. Several CB bearings. Diff fluid and shock oil several times. Couple of wheel bearings. Couple of wheel nuts. Tires, but I am due to replace the body real soon.
Gas truck--7 gallons or so. Aside from the occassional A-arm and diff rebuild every couple of gallons, nothing but the fuel and plugs. Tires, but I am due for a new body soon.