Ice Scraper for windshields
Lottery Tickets
Aromatherapy Shower Steamers
Keyboard Cleaning Gel
Mad Libs
Multitool
High Lumens Flashlight
Table top game (There are lots of options for $10 or less)
I like where you're thinking and it's great you're thinking some outside the box but much of that stuff isn't something that a bulk of people would probably not already have or they wouldn't or couldn't use and the keyboard cleaning gel is something that the employer should be providing anyhow.
Lottery tickets could ruffle feathers for people who don't gamble. And is that considered cash equivalent not to mention you need to make sure everyone is of legal age for the state (not every state allows an 18yr old for example to have a lottery ticket).
Ice scraper I don't know anyone who lives in a winter weather destination that doesn't already have 3 or 4 or 5 of them lol
Aromatherapy isn't good for people with scent sensitives plus pets as there are things that are toxic there.
We've got at least 10 different multi-tools laying around the house in multiple points (the garage, kitchen junk draw, both have the window breaking tool in the cars, etc) Most people I know have multiples of these usually because they were in a set of something else.
Everyone I know has multiple flashlights too, we like these lantern style ones that are water resistant so they've been used for power outages as well as outside when we've done fire pit nights.
Most of those stuff as an employee I would see as more things to clutter up
Hands down the favorite gift among our team was a "coupon" to leave work early on a pre-planned day. They were paid and were not required to use any vacation or PTO.
That one is nice but it would need to be run by how that affects payroll/company's finances as well as how that is worked out for salaried vs hourly employees including overtime pay. My husband is salaried and can't take time off less than 4 hours (half a day), he could leave work early but it's flexed out meaning he still has to work 40 hours that week. His overtime is straight pay. I can't remember if overtime to him is 45 hours or not but I know for sure his prior company overtime occurred at 45 hours because he was salaried. Meanwhile I was hourly and could take off work in 15 min increments and a minute over 40 hours was overtime at 1.5X the pay. It needed to be physical hours worked however. I couldn't take work home, my husband can take work home, etc.
And I actually just found out this the other day, granted it's California so they are very particular about things but a project my husband was working on the head boss for it was just fired and there could be legal action because he illegally shifted work hours around each week in order to not pay the employees under the project overtime.
OP is doing it for 100 people which is a lot. That's about the size of my husband's present job and they are actually reducing the allowable carry over PTO in a few years because financially it's a lot on the books. Plus you have to place stipulations on when it can be used to ensure you don't have too many people using it at once unless your (general your) workload can handle it.
We had one year when I was at the insurance company that you could "buy" an additional PTO day, by buy I mean you were paying for it by means of deducted payroll for donations to March of Dimes. But that company was sued by the Department of Labor due to payroll things (not paying employees for work that was deemed work like starting up your computer) which caused them to be extra careful to not step over that line. That additional PTO day only lasted one year. My guess is they had too many people do it. Another thing they would do is you could buy the ability to wear jeans on a Friday, back then you couldn't wear jeans unless the customer service goal was met the week prior. Again all these things had to be run through payroll and paid out. Likely for legality reasons.