I'd agree on the transferrable skills, labouring and garden centre work sound quite physical jobs so I'd include that.
Does he have experience of handling a till / POS system?
Customer service?
Also why he wants to work in hospitality? Does he see it as a career or just a holiday job?
Does he have a driving licence and access to a car?
Does he have or know someone with a food allergy? Diabetes? Restrictions on eating for religious or cultural reasons.
So something like:
I am seeking employment in the hospitality sector as I like working as part of a team although I can take the initiative to work on my own when required.
I am punctual and hard working. I have gained skills from my previous work experience at X I learned A B C and at Y I gained skills in XYZ.
Initially I am looking to work over the summer before attending X University to study XYZ, and I will be available to work in university holidays including Christmas day (obviously don't put this if he won't be happy working Xmas).
I am willing to work in any part of the sector whether that be in kitchens, serving tables or collecting glasses and washing up.
I have access to a car in the evening so I am able to take shifts that end after public transport has stopped running.
I have a wide circle of friends from different cultures which has given me an appreciation of the difficulties some face whilst eating out due to allergy, culture or religeon.