The IRS allows you to deduct any purchase that would be considered “ordinary and necessary” for your business. An expense has to be both “ordinary” for your industry, and “necessary” to keep your business running smoothly.
For example, if you’re a freelance writer and pay submission fees to submit your work to literary journals, you could deduct those fees since they’re both 1) ordinary for the creative writing industry, and 2) necessary in order to succeed in your line of work.
Similarly, as a rideshare driver you could deduct water bottles and gum for passengers, as well as a big portion of your vehicle expenses.
When you’re deducting a business expense, just be sure to keep track of the percentage of that expense that was used for work. If you use your cell phone for both work and personal reasons, then you’d only deduct the percentage of your bill that’s related to your phone's work usage. Using your phone for work half of the time? You can deduct 50% of the bill!