(These are just some possible answers – there are more in the text!)
…if you want to minimise disturbance to the birds and sheep, please get in touch with Tom Nicolson on this email address…
Key to the house: To be got from Tom Nicolson. (note – this isn’t a complete sentence)
Please try and leave the place better than you found it…
Make sure a rat has not stowed away somewhere. (to stow away = to hide on a boat. Stowaway is also a noun.)
Take any waste away with you.
You must bring all your food and other supplies with you…
…please bear in mind there is a considerable amount of supplies from previous visits…
It is best to bring some bags of coal and some kindling. (kindling = small pieces of wood to start a fire)
I ask people to go to the loo in the intertidal zone… (loo = toilet; intertidal zone = the area where the sea comes in and goes out during each day. The way the sea moves is a ‘tide’.)
It is best, I have found, to sleep in tents…
You obviously need wet weather clothes… (you can use ‘need + noun’)
Before you go, you will need to absolve Tom Nicolson in writing from any responsibility for anything that happens to any of your party. (to absolve someone = to say they are not responsible; a party = a group of people who are doing something together).
You’ll find some information here about useful phrases (which aren’t modal verbs) for giving instructions or advice in English.