What you actually need, by category.

Magnification range, reticle type (mil vs. MOA — pick one and stay consistent across your gear), and turret style (capped hunting turrets vs. exposed tactical turrets) are the three decisions that matter most. Match the optic to the discipline: a red dot or low-power variable for close/dynamic work, a higher-magnification precision scope for distance.

Bolt-gun / PRS: 6mm and 6.5mm cartridges dominate the competitive field for their flat trajectory and manageable recoil.

Precision AR / gas gun: .223/5.56 and 6mm ARC are the common competitive choices, balancing reliability with the accuracy the discipline demands.

Hunting: caliber choice depends heavily on species and terrain — this is worth researching for your specific hunt rather than defaulting to whatever's popular.

Factory match ammo is a fine starting point for anyone not yet reloading. Whatever you shoot, confirm your zero and collect real DOPE (data on previous engagement) with the exact lot you'll compete or hunt with — ballistics change between lots and manufacturers.

Eye and ear protection, a stable rear bag or bipod, a data book or app for logging DOPE, a wind meter if you're shooting distance, and weather-appropriate layers. Beyond that, buy for the discipline you're actually shooting, not the one you think looks the coolest.