Hello,
I agree with Wharton. 3 litter trays etc. HUGE bowl dried cat food, ditto water (never enough even though they pretend not to drink...). Also, the battery-operated feeding dish is great for two days).
Your main problem is what happens if you can't return at your proposed date - I always make arrangements for the creature 'in the event of......' etc
Another thought: if you are turning your heating off: remember cat! I have a small, low-wattage "Back Warmer" in a fleecy cover, with a timer (try Argos). My cat adores it and won't sit elsewhere.
Your cat will freeze or you will have a huge fuel bill if you don't address this issue!
Best of luck!