I've saved a lot of money when I go to conventions by volunteering. As a volunteer I've gotten free passes, free food, free con merch, and a quiet place to sit. Most conventions don't have enough staff to fully run a convention without some kind of assistance. As such, many conventions offer partial to full reimbursement or a badge up front in exchange for an attendee's time. Volunteers are asked to do a variety of tasks including but not limited to badge check, panel monitoring, prop check, autograph lines, etc.
So far for volunteering I have only been assigned to badge check and panel moderation. For badge check I sat at either the entrance or the exit to the convention area and ensured that those entering the convention area had their badge. Anyone without a badge was turned away and instructed on where to purchase one. For panel moderation I was asked to attend panels and just take notes on turn out, content, and how the presenter behaved, then hand the feedback in to the staff.
The food I've been provided has come in the form of pizza, gift cards, and snacks such as pudding cups, crackers, applesauce, fruit, and more. They also had drinks for volunteers such as energy and sports drinks, water, sodas, cold teas, etc. The free merch has been t-shirts and thermoses. And while the thermos was cheap, it will make for a great con thermos that I have no issue accidentally loosing, meaning that I can save my nicer ones for situations where I'm less likely to loose it.
The quiet place to sit has by far been the most underrated of these perks, however. You never realize how nice it is to have a place without echoing noises, screaming teens, music blasting, or other con sounds. The volunteer lounge that I've gotten to experience had a few older video game systems with quiet beeping sounds, inflatable couches and chairs, a few tables with normal chairs, and the glorious snacks and drinks. This location does not allow in the friends of volunteers, however, so don't expect that one person in your group can volunteer and the rest also get a quiet place to relax.
When volunteering I have found that most cons also are open to you moving around your schedule a bit, if it is within reason. Examples of this are that I once was scheduled for a 6 hour shift that would have covered both lunch and dinner on a Saturday. I approached the staff and discussed the possibility of me moving half my shift to a late night shift so I could get a chance to eat and take a break. The convention was extremely open to that. At another con I asked if I could move my Sunday shift to Friday for travel purposes. The convention was understanding and more than happy to accommodate my needs. Not all conventions will do this, but it certainly does not hurt to ask.
And on the topic of asking, I personally have never asked for this, but I have heard of some conventions allowing for volunteers to volunteer a few extra hours in exchange for a place to sleep in the assigned convention staff hotel rooms. So you always can approach the convention, explain your situation, and offer more time in exchange. Though at this point you may as well apply to staff the convention.
Volunteering is not for everyone by any means. Much of my convention time is taken up by working for the convention. And the exchange rate for the badge and hours are extremely low. Most conventions (an example is Ichibancon, taking place in Concord, NC just north of Charlotte, NC) require about 16 hours of volunteer time in exchange for a badge and a badge costs approximately $60. If you do the math, that comes out to you the attending being reimbursed at a rate of approximately $3.75 per hour. (That rate can change based upon the cost of the badge and how many hours are required, so make sure to do your own math.) However other conventions do require far less (an example is Queen City Anime Con also taking place in Charlotte, NC), and as little as 8 hours. This makes your return rate much higher, so closer $7.50 per hour.
For some it is a better investment to pick up a few extra shifts at their job and than not have to volunteer. However, it can also be scheduled time where you sit down and take a breather. When I volunteered at Ichibancon in 2019 I used the time to sit down, eat the food I'd purchased, and also text some friends. I was badge checking so it wasn't too difficult. When I volunteered for Momocon in 2019 I attended panels and just made sure to take notes for the staff to look at later on and thus evaluate the panels for future years.
Something worth noting for volunteering at conventions is that you could be asked to staff, and if asked to staff, in exchange for just a few more hours, you could also be placed in a hotel room and/or food provided for the entire convention. Since many conventions are part of a connected chain this can also open doors for you to attend multiple conventions a year nearly completely free of charge in exchange for just a bit of your time.