I now carry around a £5 dumbphone in my bag for when my smartphone inevitably dies on a night out (and yes, I do have a second charger at work). When I use the dumbphone as my main device, the battery lasts around two weeks.
Additionally, they are replaceable- my dumbphone (which I left smartphones for) was $20 without a contract. If I get pushed into a pool or drop it off a cliff, I won't be especially put out.
I question the validity of owning a so-called smartphone and I'm seriously considering either selling it or giving it away, because I know I'd really not miss it.