I'm going to Bogota, Salento Popayan and Pasto.
Any local food and drink is a must try?
I'm a big fan of street food too.
Disclaimer: I've not been to Colombia yet, but I have it on good authority that this is one of the most typically Colombian street foods, and I've tried it from Colombian places in other countries and it's pretty distinctive.
They're a kind of stodgy corn (maize) bread, often served with cheese. Surprisingly filling, good for breakfast or after drinking, and goes well with a strong coffee. Usually savoury, occasionally served sweet or with sweet cheese.
It also exists in Venezuela, but over there is used differently, more like sandwiches. Here are some typical types of Colombian arepa from mycolombianrecipes.com's page on arepas:
My advice is to avoid street food. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3209856/
A study in Santa Fe de Bogota, Colombia revealed that over 30% of a group of food handlers examined were carriers of pathogenic microorganism including Salmonella typhi, Staphylococcus aureus, Salmonella enteritidis, and Shigella
The report details a number of worldwide methods by which pathogens can be passed on to customers, including cross-contamination, careless food handling, disregard to hygiene, and vendors blowing air into polythene bags to ease packing food while serving the customer.