Nici Wickes has got a list of things you should have on hand this summer:
Dairy  
Parmesan cheese 
Greek yoghurt 
Sour cream / cream cheese / creme fraiche    Pantry  
Olive oil + sesame oil  
Red wine vinegar 
Tins of guava, salmon, tomatoes, creamed corn  
Sushi rice  - great for sushi & for rice pudding & risotto  Protein  
Quality sausages 
Frozen prawns 
Eggs  
Veges/Herbs/Fruit   
Bunches of parsley & coriander - I'll let you know how to store these so they last all summer long  
Garlic & onions or spring onions  
Lemons lemons lemons 
Tomatoes 
Frozen berries  
Fresh berries, stonefruit, watermelon   
Other 
Flat breads: wraps/tortilla/lebanese bread LISTEN TO AUDIO ABOVE