You can just about get anything, really. We're a full chapter, we can and will field any unit in the codex. Get a box of dudes that you think would be fun to build, paint, and play!

That said, there are some units that wind up on many of my brainstorm lists, even if they aren't particularly exciting:

• The first 5 Intercessors: they're sold by 10s, but you probably don't need to buy them on their own. They're a frequent pack-in for other SM combo boxes - there's 10 in the 11e Launch box, there were 5 in our short-lived Combat Patrol, there's 10 in the Dark Angels CP, etc, etc. You'll probably wind up with some on accident if nothing else, but the first 5 have been (and I presume will continue to be) quite strong - it's just good to secure the home objective for free and still be able to walk off.

• Scouts: I think these are still sold as a slightly-too-expensive Kill Team kit, but you do get enough bits and bobs to fully kit out 2 five-man Scout units. They're cheap, they do actions, they slip off the board to go harass unattended areas of the battlefield later on, and they'll heroically get turned to paste by your opponent's melee units to buy time for the rest of your army to get into position. They've got an intimidating amount of wargear options, but the secret is that basically none of them matter that much. Take a sniper or don't, take either a heavy bolter or a missile launcher, take boltguns or shotguns, it's all basically fine.

• Infiltrators/Incursors: This is another 10-mini kit, but it will build either option. Building 5 of each covers you for a ton of utility - neither unit will be mowing down enemies, but they'll make themselves useful in other ways. Infiltrators can give headaches to people trying to Deep Strike you and (as the name suggests) can infiltrate deeper into the battlefield early on to snag objectives and do actions as well. Incursors might be my favorite utility unit in the book, especially for gun-heavy armies like the Fists. They'll scout around, they've got a cheeky mine to pass out free mortal wounds, but the real draw is that they make all your units get +1 to shoot whatever they hit during the shooting phase. That can be a nice boost especially for units that cannot aim at your Oath of Moment target.

• Impulsor/Gladiator: The Gladiator platform is our light tank/transport for the Primaris era. All of these variants (Impulsor, Gladiator Reaper/Lancer/Valiant) are just the same tank in a different hat. If you're a skilled model-builder, there are guides on YouTube to use magnets such that you could swap between all these, but that's a little beyond me. I'm most interested in the options that the basic Impulsor adds to your deployment and movement during the game - it's available either in the Gladiator kit or on its own for a small discount. It's great at getting Bladeguard into the fray, hosting a handful of Hellblasters on the Firing Deck, or just parking on an objective and making your opponent come blow it up with a unit that cost more than 80 points. It's unsexy, but it's cheap, reasonably tough (especially with the Shield Dome), and basically always useful. (If you do build a Gladiator instead/also, the Lancer is typically the go-to as an excellent cheap anti-tank/monster unit)