The apps on my home screen are always shifting around. I only try to keep stuff on there that I know I'll use every day.
Besides the fun stuff (Instagram, Twitter, Spotify, etc.), there are a handful of productivity apps that I can't live without. A lot of apps come and go from my home screen, but there are four that remain consistent.
I keep my entire life in Evernote: Interviews, business cards, recipes, and even random stuff I need to remember like a friend's new address. I've become so dependent on Evernote, that I don't think I could do my job without it. My colleague Nicholas Carlson is an even bigger fan. He used Evernote to write an 90,000 word book.
Slack is a communications app that is slowly replacing email for intra-office communication. At it's core, Slack is a chat room, but you can also use it for direct messaging and swapping files with coworkers. It's much more efficient than email. If you want to reduce how many emails your coworkers send you, convince them to use Slack instead.
Microsoft's new version of Outlook has only been out for a few weeks, but I already think it's the best email app for your phone. It syncs with all the major email services including Gmail, Yahoo, and, of course, Outlook. It also syncs with Dropbox and Google Drive, which makes it a lot easier to email files you have stored in the cloud.