All this traveling sure can work up an appetite! It's time to figure out where to get some good eats... or at least edible eats.
All but the biggest cities offer you a more or less limited array of options. However, the small, family-owned, hole-in-the-wall restaurants that dominate Bolivian cuisine make for a suprisingly good meal. They generally only serve set lunches (almuerzos), typically a soup to start, a main course consisting of meat, rice, and starch (potatoes or yuca), and maybe a cup of pudding or something for desert. It IS possible to manage as a vegetarian, but you'd better quickly develop a taste for white rice and black freeze dried Andean potatoes (solar) otherwise you're up Shit's Creek, as they say. Also, expect a look or two of bewilderment from the staff following your alien food request.
If you're unlucky enough (or lucky depending on your sense of adventure) to be stuck eating lunch on the road, most buses will make a pit stop or two at what are vitually shantytowns set up along the highway whose sole economic viability is based on selling food to travelers. You don't even have to get off the bus if you don't want to! Merchants, typically women and children, will come onto the bus to serve you or even sell you food from the street as you lean out the window and toss down your money. Candy and chocolates are the most common item, but full meals are also served. Thankfully, over-packaged consumer products have not yet established a beachhead outside of major urban areas. As a consequence, expect any food you purchase to be served to you in a plastic bag. Drinks, soups, and hot oatmeals will come tied tight with a straw stuck inside. Chicken, fried potates and platanos will all come mixed together and typically drenched in mustard and ketchup. "Carne" is also available, for the more daring soul. (I'm still not sure exactly WHAT it was I ate on the road from La Paz to Arica... the lady insisted it was beef, but by the looks of it, if it was even beef at all it was a 10-year-old dairy cow with "one hoof in the grave," as it were. My guess was llama... There sure are plenty of those suckers to choose from in the Andean Altiplano.)
Big cities give you a little more wiggle room, but where's the fun in that, eh!? La Paz , for all it's immensity, actually doesn't stray much from the "comida tipica" mentioned above, considering it's working-class majority indigenous population. Although the touristy downtown section does offer some vegetarian and Continental options.
In contrast, considering its relatively small size, Cochabamba is King of Kuisine! Cochabambinos love to eat, I've heard, and the myriad food choices available in this fine burg relfect the entire spectrum of Bolivian cuisine. European/ Colonial Spanish cuisine from Sucre, lowland Camba style dishes from Santa Cruz, and of course highland "comida tipica" can all be found here. Not to mention a few decent Italian joints. (It's no Staten Island, but...)
Moving further down in altitude, Santa Cruz makes up for what it lacks in sight-seeing and political correctness with THE MOST gastronomical diversity in the whole country. Classic Camba food is meat, meat, meat!!! Bolivian or Argentinian cuts are both available. (Casa Tipica de Camba is the campiest eating experience you can find. Sort of a Cruzeño Chucky Cheeses'. The waiters are decked out in overdone traditional Camba wear and singers croon to uneccessarily loud synthesized Casio beats.) Brazilian food is also huge here, considering the large expatriot population. (This joint called Rincon Brasileiro literally serves grub by the KILO.) There's even a Japanese restaurant! Werd.
So that's pretty much that when it comes to food. If you're trying to stay veg, stick to the cities. If not, it's llama time! But then again, virtually none of the livestock down here are raised in factory farms, so that should take away at least some of the guilt you might otherwise feel as you tear into sweet, juicy, tender Argentinian cow flesh. Now, whether your intestinal tract can handle the sudden meat-bomb gut shock is an entirely different matter...