Let’s start with another question:
Where are you going to be shooting? Square range with wind flags and a target tender to mark the hits with a spotting disk? The middle of the desert, a corn field, the woods? If it is the later, a steel target greatly helps as you get instant feedback on hits based on where the paint gets knocked off. Also know that if you really want to learn to read / shoot in the wind, you need to shoot in non square range enviros, on blue bird days AND shitty weather, most importantly - in a variety of places. Wind is as much an art as it is a science.
The basics - rifle / ammo / a means to chrono and determine drop and drift (record this) / a means to call wind / a means to determine distance / a means to correctly determine dope / a means to spot hits and misses / a means to haul your gear.
Priorities? A spotter with a ranging ret is what I would focus on first. Buy a pretty good one - a first focal Loopy with a TMR would be a a reasonable minimum standard. You need learn to read mirage and a spotter is the best means to do this. Ranging - the ranging reticle will not be as accurate as an LRF, but with practice you will be within 5% on known size objects out to 1k. (Mathematically workout how a 5% error impacts your dope) Not saying your aren’t going to have a lot of work to get there - but you will get there if you consistently put the work in.
Wind meters tell you how hard the wind is blowing where you are. It gives you a reference at a single position. A spotter will allow you to read mirage at multiple positions. From there it is about being observant - listening for changes in the wind (suppressed shooting) or watching for changes in the amount of movement in vegetation along the bullet flight path, changes in mirage, understanding the timing of the day’s wind cycle. Wind meter, get one that will give you atmospherics when you can. Use those atmospherics to plug into the ballistic software that you carry on your phone. As a manual backup - get yourself a Field Density Altitude Compensator by Adaptive (slide rule).
LFRs - yeah, get one when you can, they are more accurate and faster. Otherwise, learn to use you spotter with a ranging ret and confirm it against a topo map. Can’t do that yet? Use a GPS. Both the map (with a roamer and the GPS will put you within 10 meters). . Also get a Mil Dot Master - it is faster than a calculator, but you should carry a calculator and fully understand the math for MOA / MILs (and be able to think and work in both) in terms of slope, leads, drift, and distance. Commit the constants for all of these calcs to memory.
While you can shoot off of your ruck / pack, and place the butt of the rifle in the crook of your wrist while you hook your thumb in the collar of your shirt (and you should practice this just b/c it is part of being a rifleman) a bi-pod and a sand sock are more accurate. You can make your own sand sock of an old pant leg and some poly pellets.
Get, learn how, and become proficient with a sling.
Pads / prayer rugs - I have them but don’t use them. I prefer a tarp if is raining and / or wet but use nothing if it is dry. I do wear hardshell elbow pads.
Tri-pod - in true field conditions a full size tri pod is very handy. You can trim the last leg section to cut down on some weight and bulk. Take a piece of sheet metal and fold it into a U, then duct tape some sleeping pad to the inside of the U and affix a proper mount so you can attach it to your tri pod head - now you have a shooting cradle.
Snivel gear - terrain, weather, and personal needs will dictate.
Training - you’ll flatten the learning curve if you can get someone that really knows teach you. If not, Snipershide has an online training program, if nothing else - read, think, dry fire.
Reloading - you’ll produce more accurate ammo than you can buy and for less $ if you reload. It will also deepen your understanding of ballistics.
There are so many doodads that you buy, some of which help and some of which don’t add much. On the cheap, I start with the basics above and once you have a baseline of skill, you can pick what you need to add.
Good luck