I've written countless blog posts about watching your spending on police stuff, advising you to see if it's within policy, if it's a want rather than a need and other fatherly advice.
There are a few things that should not be skimped on, provided you have to buy them. Some departments issue certain things that others do not; and you might receive an equipment reimbursement for certain items. So what can you invest in and not scrimp on? I'll leave firearms out of this article.
Footwear is an over-looked item. Some departments issue or demand an officer have the shiny low quarters for court and dress. Fine. If you want me to wear them, then issue them. You can't do real policework in shiny shoes. If you're allowed to wear boots on patrol, these are extremely important.
Comfort is your first consideration and safety is second, especially with ankle protection. Ankle sprains are one of the most frequent patrol injuries. If your dawgs are barking at the end of every shift, you'll need to review what you are wearing. Some like low cut, mid cut and high top. Zippers, steel toes, waterproof, insulated, and quick lace are all what you feel fits your needs.
Hundreds of kinds of shoe soles, some with enough knobs to climb a mountain, again your choice. See what the other officers are wearing and where they get theirs from. Cops will always seek a dealer with a better price. Big thing here is your comfort, I don't care what looks cool; comfort is first and safety second. The big hint here is to follow the manufacturer's recommendations on care. There are some materials that require special treatments and care.
Glasses are a needful item, especially sunglasses. I'll tell you to buy some eye protection for the range bag, no more using the communal goggles that are scratched up. Your range scores may go up a few Xs. Sunglasses will have a policy attached, so read and heed. Good quality sunglasses are going to be pricey. Look for good UVA/UVB protection, polarization and safety.
Sunglasses are not for summer only but year-round. Review the safety ratings of the glasses you're researching. Some great eye protection has evolved from our military. The tactical glasses offering high impact protection are great, and they look cool. You only have two eyes, protect them. Here too, proper care and treatment will keep the lens clean and scratch free.
I could go on about other needful things for your patrol world. Always consider comfort and safety. If you have comfortable and happy feet, you will walk around the building and find that burglary or catch the perp that's trying to run.
If you can see comfortably, you'll fatigue less and maybe save your precious sight. I occasionally hear of the pennywise-but-pound-foolish cop who wants to wear cheap sunglasses and second-rate footwear. Face it, the money savings could be great but what good is that if you are not feeling great and looking tactically cool.