Must Haves

All In One SEO Pack
Out-of-the-box SEO for your WordPress blog.

WordFence
THE security plugin.

WP Optimize
Clean Up / Optimise your WordPress installation.

WP Super Cache
WordPress Caching.

WP Smush It
Optimise graphics files.

WP Migrate DB
WordPress database migration.

Used in Specific Circumstances

Advanced Custom Fields
Provides simple flexibility.

Post Types Order
Provides simple and easy sorting.

Superceded

These we still use occassionally, but simpler to build on the fly:

Contact Form 7

These we no longer used as they’re all done by All in One SEO:

Google Analytics for WordPress
Google XML Sitemaps