Food is cheap in Krabi, and I advise not to waste your time in McDonald's but try different cuisines on the street especially night markets. I checked some of the best food joints around on Trip advisor and found The Pizza company to be a good place, I tried their sausage spaghetti and it was delicious just as I like not too cheesy and tasty.
You must try the night market food stalls which offer a wide variety. Few things that I would advise to try are the Buns, rice crackers, Pad Thai (obviously), bamboo drinks and fish food.
There are different night market centres across the island, during my stay, I found two near me, the first one was right adjacent to the Ao Nang beach stretch and the other one at the city centre. As I was anyway near the beach, I went to check out the one at the centre of the city.
It took me 40 minutes to reach the night market in city center from the beach and it cost me 300 baht to & fro, which is fair deal.
Night market has entertainment arena where you can grab some bamboo drink and hot buns or pad thai and enjoy Thai music, dance, kids performing to traditional songs. You can also, get some souvenirs from the market as they are very cheap compared to Bangkok.
The best way to save some money on transportation is to stay near the beach side which can be easily be accessed by walking. And another way is to use the hotel tuk-tuk services which drops off and pick up at a spot to a hotel at no cost. Just make sure you know the timing of the hotel tuk-tuk services as they are available at an hourly basis. This way you will surely save 200 baht which you would be charged from the beach to the hotel, so make sure you are aware of this.
Also, as mentioned for Night Markets in the central Krabi you can always book the cab service from the hotel or from local agents which would cost you from 200-300 baht or cheaper.
The airport in Krabi is nearby so if you need a cab service to pre-book it from the local agents which will be cost effective than booking a complete cab for yourself. Sharing a cab would be very cost effective and would round up around 100-200 baht.
Hope this helps in planning your Krabi trip, do write to me in case of any query about Krabi and follow my travel through my Instagram