Definitely seconding the Garmin Edge 1030 recommendation. The Edge 530 is also a fine choice and can use the same external battery or charge from a dynamo hub or external battery with a micro-USB plug while in use. I exclude the Edge 830 as it's primarily a touchscreen device.
Also worth consideration is the Wahoo ELEMNT Roam, tho it doesn't have the cool on-mount external battery pack option as the Garmins.
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As to my favorite bits of kit, I always think of "kit" as clothing and such. I'll go with that, and then recommend bits and bats for the bike.
My favorite helmets these days are by Kask. Build quality is excellent, ventilation is great. And they simply work. No, there's no MIPS, though its efficacy at higher speed crashes is debatable (it also can yank hair out of your scalp under normal use). I own two Kask Protone units and love them.
I've found that the best bang-for-your-buck in bike shorts these days is from The Black Bibs, which is a division of Starlight apparel. The chamois in them is lovely: not too thick, well made, stays put. The build quality of the shorts is top notch as well. And they're affordable: the basic model is $40, the more deluxe model is $65, the winter model is $70. And they come in black or navy: simple colors that go with almost any jersey.
I love the fit and finish of jerseys from Velocio and ORNOT: nice race cut, the cuffs don't roll weirdly on them after washing, and fun color options. They are not cheap, but the build is worth it.
I also love the Rapha Brevet Gilét, a bright pink vest that's lightweight and super visible. I do a lot of riding pre-dawn and post-sunset, and this compact vest gives me amazing 360° visibility when the light is low. It's also fairly breathable, which is a concern living in humid country. Mine has stood up to 2+ years of abuse and is still essentially as good a new (and Rapha will repair or replace it if it wears prematurely).
I wear gloves, many different models. For short finger I'm usually wearing Specialized Grail or random Giro models. For long finger, 100 Percent or Pearl Izumi for lightweight, Craft or Specialized for winter weight. The latter are a lobster style for maximum warmth.
Socks? Love socks! I use many pair by Ridge Supply, a few from Heel Tread (good for the petrolheads in our midst, as all their socks are car themed), and light wool socks from Sock Guy and DeFeet. I'm moving more toward lightweight wool socks all year long these days due to their anti-funk properties.
As far as other headwear: Halo headbands are awesome and work well on this sweathog, and Rothera caps are the best cycling caps I've ever used. The headband is wide (read: no band pressure on your forehead), and the designs and materials they use are tons of fun. Nice little company, too.
For bits and bats on the bike:
I really love my Spurcycle bell. I have one on every bike I own. They're made in the U.S., are brass, and have a clear peal that can cut through most car stereo systems or noise cancelling headphones. And they tend to also mix well with fellow riders' sensibilities, unlike an air horn. I ride in urban settings every day, and this little bell has saved my bacon more than once.
The Lezyne Road Drive mini pump is a lifesaver when I have a flat. Sure, a CO2 cart is quicker, but it bleeds quickly and isn't very eco friendly (tho I do recycle the canisters). The Road Drive pump has a small hose that allows it to fit into weird valve setups, gets a tire up to pressure in about 80-90 strokes, and is built like a tank. The nozzle screws onto a Presta valve, so I've found that some brands of tube (Continental, I'm looking at you) tend to have the valve core back out when you unscrew the pump hose. Annoying, this. That said, all of my Conti tubes now have a bit of Loctite blue holding in the valve cores.
I love Ergon SR saddles: well made, lightweight, comfortable for my sit bones on really long rides. I also have a Brooks Cambium C-15 on my hardtail MTB/gravel bike and it's super comfy, though I've broken one of these (replaced under warranty) so maybe it's not my ultimate choice for longevity. Just keep an eye on the rubber on those, as it can split.
I'm a fan of Fizik Microtex tape. Can't stand the tacky tapes, but the faux leather microtex stuff is lovely.
Big fan of Arundel bottle cages, both the composite and carbon ones. They hold bottles more surely than any cages I've had since Specialized's long-since-discontinued heavy aluminum MTB cages.
Also love handlebar bags from Rickshaw Bags: classy look, simple attachment, hold a lot of stuff, very stable. And my under seat bags are all Speedsleev Ranger models these days: great design.
