What's the best work experience to get for medical school?

Look at things you already do and think how that may be applicable to being a medical student/ Doctor. For instance, I had a part time Job working for Lush which would involve talking to customers about health concerns like greasy hair, spots or oily skin, understanding their ideas and concerns and recommending products which may be suitable for them based off the information given. This helped me to develop my interpersonal skills and understand what is important to others, as well as my communication and confidence. If you want to do something medical, you have to try very hard as a lot of places aren't willing to offer experience so apply to as many GP surgeries as possible for instance, or care homes etc. What you do is not as important as what you learn. If you spent four years in theatre but took absolutely nothing away from it, that isn't as valuable as someone who spent an afternoon with a GP, and learnt about patient centred medicine, understanding patient's ICE, the roles and responsibilities of different healthcare professionals.
Be accepting to take absolutely anything that is offered to you and think actively about how you can learn from it. If you are struggling, Gap medics offer work experience abroad which you pay for however some companies are willing to support you financially if this is an issue. To finalise, look at what you already do and think about what skills and qualities this has given you and how they are applicable to medical school, then think about what you haven't learnt or developed and look for experiences which could provide these. For instance, if you're a brilliant team player but never had the opportunity to lead, think about doing a DofE expedition and talk about how orienteering your team presented challenges like conflict resolution but this experience helped you to develop confidence and leadership. Or if you know you want to work in healthcare but your not sure exactly what you want to do, contact your GP and ask if you can talk with staff their for 10-15 mins about their job and see what you learn and what you like.