• Reloading Press
• Dies
• Calipers
• Scale

Everything else, like the various press options and reloading accessories, just makes reloading easier, more enjoyable, and more efficient. (And of course you'll need bullets, primers, powder, etc.)

A few examples...
You don't need the press's options to begin reloading, but the Strong Mount, Bullet Tray, and Empty Case Bin & Bracket really outfit the press nicely, and, improve reloading speed because the bullets and empty cases are now right next to the press's shellplate.

You don't need extra Primer Pickup Tubes because the press comes with one Primer Pickup Tube for both large and small primer. But if you buy an extra 4-pack of Primer Pickup Tubes (each tube holds 100 primers) - now you can load 500 rounds without stopping to load a Primer Pickup Tube.

You certainly don't need Digital Calipers to check the dimensions on a loaded round, or an Electronic Scale to calibrate the Powder Measure, but you will probably enjoy the "increased reading speed" they offer over Dial Calipers and a Balance-beam Scale.

To sum up...
The "Never Reloaded" Packages include everything you'll need to start reloading in one caliber with the RL 550B. There isn't anything "missing" (you'll wish you had later) in either of those two Packages.

The "Currently Reloading" Packages include everything press-specific you'll need to start reloading with the RL 550B, but still allow the option for you to add additional accessories to each Package.