Seeds are good. I particularly like toasted linseeds but they're a bit difficult to eat without leaving a trail! Do yourself a favour and get the shelled sunflower seeds or you'll spend all day fiddling.
Other good things are pork crunch (those pork scratchings that are a bit like Quavers), nuts, biltong, little cheeses etc. I quite like those kabanosy too that you can pick up in the Polish bit of the fridge in the supermarket.
Incidentally, does anyone know if you can get shelled pistachios? I LOVE pistachios but they're a bit too fiddly for me to graze on at work and you end up with a big pile of shells.