I've enjoyed reading through everyone's responses and have added a ton of things to my cart/wishlist...

Amazon is my go-to for pretty much everything --- phone cases, screen protectors, batteries, cat food, random household things. Off the top of my head, my favorites:

• Lightning/micro-USB charging cable. I love that it can flip between the two charging ports; I can use one cable for my iPhone and Kindle, finally! We've replaced all of our electronic cables with these.
• My Kindle Voyage. Love, love, love it! It's always with me.
• Zinus SmartBase mattress frame. Sturdy, quiet, and super tall for underbed storage. Enough said!
• Packing cubes. These are soft-sided packing cubes, which is great for me since I can cram more things into them. I get so much more suitcase space back, and it helps keep things organized once I'm at a hotel.
• Stainless steel sink caddy. Sponges left in the sink drive me crazy! I like this one because it also has stands for scrubber brushes and the coordinating soap dispenser (which I also bought) fits nicely in the compartment.
• Programmable cat feeder. We've tried so, so many automatic feeders for our cats. The feeders either crap out or the cats figure out how to get it to dispense extra food. This one though --- it's been going strong for 2.5 years and the little jerkbags can't get their paws up the food chute; not that it matters, because portions are on a conveyor belt inside the feeder. You can set multiple feeding times, adjust portions for each meal, and it's super easy to refill thanks to the lid on top. We have a power adapter for it... the manufacturer didn't have the factory one listed at the time (it's separate) so we got a generic multi-purpose one that works.