First, the frugality. I had earned ~$12,000/year as a grad student so when I got my first job out and bumped up to $50,000, I kept my previous budget and put all of the extra toward student loans (and enough to retirement to get the match). This budget, as you can imagine, was extremely bare-bones (no internet service, no eating out/processed food, no travel, etc.), but totally livable because my hobbies have always been cheap or free, like reading library books, hiking, and having friends over for dinner. I had to bump up my budget when I got my current job because cost of living is somewhat higher here, but I earn almost $40,000 more/year and my new budget is only about $10,000/year higher, so that's a net win for my balance. I was used to living as frugally as possible as a student and have only slightly increased my standard of living now that I earn many times more per year. (I do have internet at home now, which I'm not sure is a good thing. My hobbies have taken a hit.) I'm actually grateful that I started adulthood earning so little, because I never got used to "adult" things that friends seem to have a hard time eliminating from their budgets. Now if I decide to include them, they'll be a treat instead of a given (until hedonic adaptation takes over).
As for the side-husting, the major categories were short-term extra jobs/consulting in my field (which actually helped my career growth too), pet-/house-sitting, and selling books and random stuff on eBay/Amazon. I fell into the latter by accident. When coworkers would retire or move to a different job, they would often leave quite valuable books behind for free, just to be spared the bother of moving them. I always made sure that nobody else wanted them before I sold them. I would also sell my own books and flip books I found at garage sales (but not library sales, because I felt that violated the spirit of things). A single flipped garage sale textbook often yielded $30-$60. Downsizing before my last move, I sold a decorative object from IKEA that I bought in middle school (for like $15, I think) for over $100 on eBay. I really dislike the selling process, but between the two sites, I probably made $5,000 over a few years. (I could check my records for exact numbers.) I also disliked the pet-/house-sitting because I'm a homebody (and picking up poop- yuck), but it helped out people I knew and paid between $200 for a few days and $1000/week, depending on the client/number of animals. I also did random gigs as they popped up; I made a few hundred for participating in a friend's dissertation study under some very uncomfortable laboratory conditions. All of this money went toward my principal.
Any extra money (cash gifts, credit card cash-back, tax returns, cashed-out unused vacation time, quarters I found on the ground, etc.) went 100% to my balance, too. I was surprised to see how many little occasions like this happened.
As for the actual mechanics, I paid my eight loans off highest-interest to lowest-interest. I had minimum payments automated to get the interest reduction, then made a bonus payment the next day on the loan I was currently attacking. I had a minimum bonus payment budgeted, then included any extra. I made a spreadsheet tracking my loan balances, interest rates, regular payments, and bonus payments so everything would be spent as intended. Any categories I underspend in my monthly budget meant a bonus payment, which made it really motivating to cook out of my cupboard or ride my bike rather than drive somewhere. I would also put any extra money in my checking account (beyond my comfortable cushion) at the end of each month toward the balance. I think the slow and steady progress of the automated stuff was key, even if the giant extra payments from side-hustles, etc., moved the balance a lot faster.
This sounds really obsessive so I do want to restate that I had a good life through all of this, with friends and hobbies and satisfying work. It just felt better to, say, cook a pot of soup with friends and make a bonus payment than eat out at a restaurant and spend my weekly food budget in one meal.
I hope that's helpful! Let me know if you have any other questions. And good luck with your debt paydown! It feels so overwhelming at first but I promise that as you make progress, it really feels like it's snowballing and getting easier and easier. Getting from, say, $80,000 to $70,000 felt like a monumental effort, but I barely noticed the last few $10,000 chunks because everything was automated, I had so much momentum, and so many of my previous interest payments went toward the principal. You can do it!!