You'll want one of your own. Medications, personal items you want to have. Not general line items like clothes and meds. Specifying is important. Write down stuff like 1 week of anti allergies meds, 2 pairs of pants, 6 t-shirts etc. You would think that there's no way you would forget something important. Then you remember on the way to the airport and it'll ruin the start of your trip.
Calculate based on how long you intend to be overseas to see how many clothes and meds you need. If you have an essential medicine like insulin pack extra in case delays happen. Have emergency medicine like for fever and diarrhoea just in case.
Portable charger and also your own wired chargers. Check what kind of power points the country will use and buy an adaptor if needed.
Buy travel insurance. If you have a delay you will need it. Check what the insurance covers as well to ensure it meets your needs. You mainly want something to cover last minute cancellations and flight delays that could force you to spend more than you intended. But also stuff like medical repatriation, lost luggage etc.
Get the details of the nearest embassy for your country. Write the contact details down so in an emergency you can get in touch.
Anyway, don't stress. 99% of the time all this won't be needed but for that 1% the extra effort you put in to have this ready will help you handle things better.
Thank you for letting me realise he's updating new stuff. His work is always such a treat and we're getting more!