~ $10 / Stocking Stuffers
Uniqlo Airism Mesh undershirts (aka baselayers) - great for indoor and as a base - https://www.uniqlo.com/us/en/men/airism
Nuun (or other) - sports drink tabs
Packbands / Pacbands - If you carry a top tube/frame bag on your bike and use straps, these are nicer than the velcro ones. They clean easier, don’t slide around, and come on/off easier. Only issue is that they are a bit thick and expensive https://amzn.to/3qr0PTT These might also be good, haven’t tried them - https://amzn.to/3opsHG6 (another affiliate link - just earns me $30/qrt to spend on bike stuff for a suggestion I’d make anyway)
~$25
Pro hex ratchet. Ratchet small enough to carry with you, handy enough for the shop - https://amzn.to/3fYLmpl (affiliate link)
Zensah arm and knee warmers - from the people who brought you those running calf warmer things. These are better than most cycling-specific ones because they are thin, light, have a flexible temp range, and come in a lot of colors - https://www.zensah.com/
Under $50
These are the best glove insulating liners I’ve found for winter cardio because they create air pockets under your glove, letting air circulate, preventing your hands from wetting out from sweat. Pair these with a +2 size oversized shell glove and you’re good for winter. Black Diamond GridTech Medium or Lightweight (get one of each so you can swap them out should they get wet)- https://amzn.to/39yhE9t (affiliate link again)
Garage bike stand - great for in between uses or while washing - https://amzn.to/39t9S0x (affiliate link)
Gore Windstopper gloves unlined - most used piece of kit I have. https://www.gorewear.com/us/en-us/gore-tex-infinium-stretch-mid-gloves-100655.html?dwvar_100655_color=9908&cgid=gw_men_accessories_gloves