I think everyone knows I travel with a few kg of tech. To be honest the only two things that were indispensable apart from my mobile phone were a rechargeable battery pack and a SIM card with near unlimited European roaming (this one works in Asia too)
The battery pack meant I never had to worry about my phone running out, I think this one will charge my phone 6 or 7 times itself. It kept 3 of us juiced up the entire day and the SIM card meant I could use the phone anywhere without having to worry about finding free wifi or waiting till back in the hotel or apartment (which often had dodgy wifi anyway).
This particular SIM card had 12gig data on it per recharge. It has some fair use policies that would impact you if you used it like I did over a 4 month period outside the UK, but for a month it’s effectively unlimited, and hey, a £20 recharge costs the same as a brand new sim, so just buy 2 or three sims if going for a few months.