The Envelope System--for budgeting your paychecks and staying on budget. This was actually how I saved up $630 for a computer and $350 for a new aquarium at the same time... then I stopped doing it. Maybe I should start again.
With Canon cartridges, you just press and hold the "Stop/Reset" button for five seconds when it says you're out of ink. You need to be sure to remove the cartridge when it's actually empty, otherwise it could damage your printer. Also, don't run maintenance when a cartridge is empty. Once you replace it, the printer will begin monitoring ink levels again.