For protein: Costco carries 120-calorie snack packs of beef and turkey jerkey. Easy to carry in purse, in car and keep in desk drawer. V-8 Juice: 5.5 ounce fits in backpack, or 11-ounce (70 calories) cans. A banana or apple with a few almonds. I read that peanut butter and almond butter can now be ordered in 100-calorie packs, which can be used on a few crackers or cut veggies. 

I have no idea if they're actually good for you, but I completely dig the new Clif Nectar bars.  They have the texture (and color) of something good for you.  Here's a link to the nutritional info.  I do see that they have about double the usual fat of a Clif Bar.  Worth it though!

Personally I think snacking during the day is more a habit than a requirement for keeping energy up. You're not going to fall over just because you don't eat for two hours (honest). As an amusing example of a similar habit that is funny, I've found that a majority of workers here in China are convinced they need mini naps (15 to 20 minutes) at their desk after lunch in order to complete the day (yes like in Kindergarten!). The fact is of course that they don't, but they've built up the habit and have convinced themselves they need it.

Great question! I like to keep nuts, dried fruit and some protein bars in my office desk drawer for my 3-4 PM munchie attack. I also like hummus and wheat thins-yum!

I eat a balanced 200 calorie snack every two hours of 20g protein, 20g carbs, and 2g of "good" fat. You can do this with fruit, nuts, and cheese. Jerky is a good source of protein as well or cottage cheese or some yogurts (watch out for the sugar). Greek yogurt is especially good - find it at Trader Joe's. I am fond of Myloplex Lite and Control bars - watch out for carb content in some of the "health" or power bars on the market.

Try to eat carbs and protein. For example, I will eat a few nuts and some fruit. Or a Kashi granola bar is good, too. Jicama, carrots, cucumber - any vegetables are good, but always pair them with some protein, even tuna fish (I eat it straight out of the can) so you stay fuller longer.

I like carrot sticks, and pecans, which is also good for lowering cholesterol

Yogurt.

One week I woke up earlier than usual and took my dogs for a walk. I was surprised at how much more energy I had throughout the day, and it wasn't a strenuous walk either. Took a total of 20 minutes, which is probably the same amount of time I would spend looking for junk food in the work cafeteria.