Android Device Manager (from Google): tracks your phone if you lose it. Install before you need it!;
Call Confirm: not necessary, but useful if you're prone to pocket-dialing;
Gsam Battery Monitor: if you care about tracking your battery stats;
Google Keyboard, or Swype, Or SwiftKey: I didn't care for the stock keyboard (currently using Google Keyboard) but it's a matter of taste;
Our Groceries: shopping list app I've been using for years;
Google Opinion Rewards: get from Google for answering brief surveys ($ is credit in Google Play store). I've racked up over $60 in just over a year;
Textra: if you want to try out a different messaging app, Textra is a good one;
Waze: excellent navigation app with real-time traffic and police reports.