Top King makes the best shinguard on the market, unless you’re really having problems with kick catches causing them to slip - then get the Fairtex grappling shinguards.
Gloves are a personal thing. I find Everlast gloves to be absolute garbage and I REALLY don’t appreciate people wearing them for sparring.
For sparring, 16oz is the standard.
Gloves with IMF or similar padding is probably ideal: Winning, Ringside, RingToCage, Top Ten, Title Gels, Rival.
Thai brands are also not bad: Boon, Fairtex, Top King, Twins, Windy, Raja, King, FBT, etc.
For bags & pads, it’s usually smaller gloves or gloves specifically labeled “super bag gloves”.
The following companies make awesome super bag gloves: Grant, Rival, Ringside, Title.
I’ve also had a lot of luck with Thai brands in smaller sizes (between 10 and 12oz).
Mexican gloves are typically if you want to bust someone up real bad in sparring.
Depending on the brand, they can be okay on bags & pads (Reyes, Seyer, Zepol, JC Pacheco, Campeon, etc).
Top King and Fairtex make some of the best thai pads on the market. Also notable are Twins and Ring to Cage.
Belly pads, I like fairtex & boon the best, but you really can’t go wrong.
Chest guard - I recommend whatever you can get from martialartsmart. It’s not common to wear them in muay thai; amateur muay thai that requires them is a pretty recent development.
Focus mitts, I’ve always had good luck with Ringside, but Rivals have been great, and Titles will do in a pinch.
Headgear; I’ve had great luck with Fightgear (a Ringside subsidiary). Rival, Winning, and Reyes make the highest rated headgear. Title is solid too.
Mouthguards: Gladiator is probably the best custom. I usually go with Shock Doctor.
If you have any questions about a particular gear I can try to help.