Genuine Innovations G2644 Proflate CO2 Tire Inflator https://www.amazon.com/dp/B009F94MTM/ref=cm_sw_r_cp_apa_gywqBbJHFCREW

Something like this should work well. Honestly, your local bike shop or REI will have a good selection of options.

CO2 is ideal for emergency use, quick, compact and lightweight. Generally, most tires only need to be topped off every couple of days, so you can probably find a shop pump or compressor for top ups while touring.