Salad, I just took a look at my cheese block (just a normal one from Aldi), and its totally preservative free. I swapped DS from cheese slices to block cheese without any issues.

As for other snacks that are "safe", I know Sue Dengate says Arrowroots are ok. Also, you can make your own chips from pita bread (just make sure it doesn't have preservative 282 in it)- cut it up, spray a bit of oil over the top, sprinkle with a little salt, and pop in the oven for like 10-15 minutes. Easy and yummy. You will find heaps of ideas in Sue's book too.