I have a Vue 2 project that has many (50+) single-file components. I use Vue-Router for routing and Vuex for state.
There is a file, called helpers.js
Import it in the main.js file just like 'store' and you can access it in all the components.
import Vue from 'vue'
import App from './App'
import router from './router'
import store from './store'
Vue.config.productionTip = false
/* eslint-disable no-new */
new Vue({
el: '#app',
store,
router,
render: h => h(App)
})