This is an extremely subjective question that you will get a huge variety of answers on. What it comes down to is deciding what kind of competitions you are going to do and what works for you. But here is a rundown of what I have finally come up with as a good kit that has helped me consistently place well.
Rifle - That is up to you. What you like and your style (BA vs auto, Stock vs Chassis, Ect.).
Scope - For the money I really like the Viper PST Gen II's. For NRL22 I like the 3-15 (only shoot out to 100 and normally some offhand makes 3x nice), since I am mainly shooting PRS/NRL22X now I will likely go to my 5-25 soon. Both of mine easily parallax down to 25
Base/Rings - I have a 25 MOA base on mine and I am using Burris XTR rings with the changeable inserts to get an extra 15moa I believe. That gets me to about 400 yards w/o hold over.
Bipod - Any solid bipod that can cant and pan.
Bag - I use a Wiebad Mini Fortune Cookie but there are other options out there like the Gamchangers that work extremely well. Some guys keep multiple bags around, but I like one.
Sling - I like the Armageddon gear that has bungee over the shoulder because I do not like to cuff it to my arm.
Ballistic App - The cheapest investment with the biggest payoff. I like Strelok Pro myself. It is easy to use and you can true both velocity and BC at different ranges. If the COF is available before the match which most are, I will have all of my yardages setup under the correct stage the night before. During the match all I have to do is update the weather and I know what im dialing.