Cacher is the code snippet organizer for pro developers

https://wordpress.org/plugins/slicknav-mobile-menu/   and   http://slicknav.com/ (gets great reviews - will try this!)

http://robincornett.com/downloads/superside-me/ ($30 / year)

https://phpbits.net/plugin/mobi/ ($11 on Envato)

https://en-ca.wordpress.org/plugins/responsive-menu/ (slides in from side or top)