Order is half of life - even when traveling!
I assume that we always travel with someone. If not, I would definitely plan for this, because there can be so many situations where someone trustworthy is extremely helpful.
When traveling in Switzerland, it makes sense to always have your disability ID with you, as it is necessary to show one here and there in order to receive a discounted rate. When traveling abroad, the hand / power wheelchair was reason enough to grant the discounted rate. In some cases, however, a disability ID from the country of travel may be required.
When traveling in Switzerland and certain countries in Europe, it can be helpful to obtain a so-called Eurokey (www.eurokey.ch). This gives you access to over three thousand barrier-free toilets. There is also an app for the mobile phone, on which the nearest toilet can be found with Eurokey.
If not already available, I would take glass straws (e.g. from Halm) with me for trips of all kinds. These are hygienically very good and easy to clean. Usable straws are seldom available on airplanes and due to the increasing ban on plastic straws, useful straws are increasingly in short supply even in restaurants.

For longer trips, it is advisable to bring an inflatable neck pillow with you. This allows the head to be kept in a comfortable position without great effort and prevents the head from tilting forward while sleeping and causing an uncomfortable stiff neck. An inflatable neck pillow has the advantage that you can adjust the optimal posture by adjusting the amount of air you fill.

You should get a written confirmation from the doctor with a detailed list of the required medication in English. I would take this confirmation along with the medication in my hand luggage. Countries with very strict handling of narcotics (e.g. USA or Asia) could cause difficulties without a confirmation. Medicines in checked baggage could cause customs to conduct an identity check, which can be time-consuming. The amount of medication should cover the entire trip including a small reserve, as identical medication is not always available abroad. This way there are no tolerability problems and prescription drugs cannot be obtained with the existing prescription. Covering costs through health insurance could also be difficult.

In order not to be left behind on arrival, I recommend to charge the electric wheelchair completely before departure and taking a separate power adapter for the charger with you, suitable for the travel destination.

For the hand wheelchair, I recommend one or two spare wheels with suitable tools and a small hand pump for the tires. I personally have a spare tube with me. One of my wheels broke in Australia and I had no chance of finding suitable spare parts on site ...

Public transport such as buses are not always wheelchair accessible and taxis are hardly available for wheelchair transport, and if so, long waiting times (hours) without prior notification. You also have to expect that two taxis will be needed, as the space for the wheelchair is usually at the expense of the storage space and sometimes the back seat.
Therefore I would definitely clarify the transport options (bus, taxi, rental car) for all transfers while planning the trip and book them if possible. When booking, it is essential to state the size and weight of the electric wheelchair including person. The amount of luggage including the hand wheelchair should also be communicated so that the service provider can safely plan enough capacity (possibly a second vehicle).