911 is 066 in Mexico, unfortunately it does not work on cellular phones.

Medical
24 hour medical emergency: Hospital Catemaco, 1 mile north on road to Montepio. 294 943 1834
24 hour pharmacy: no reliable one in Catemaco, but available at central plaza, San Andres Tuxtla.
English speaking physician: Dr. Ganzoni - 294 943 0758, makes house calls
Reliable Dentist: Dr. Figarola Mata - 294 943 0399, Calle Jaime Nuno 1, near Cerrito, no English, though.
Laboratories: at least a dozen of them.
Pharmacies: dozens, recommend Farmacia Roma for brand names, Dr. Simi for generics.
Veterinary: The best one is in San Andrés Tuxtla, Dr. Gaitan, 20 de Noviembre 44, 294 942 3995.

Police:
Delegación de Tránsito - State Traffic Police - 294 943 0829 - usually brown or white shirts
Policia Municipal - City/County Police - 294 943 0055 - SWAT outfits
Policia Federal Preventiva  - Federal Police - 294 942 4339 - SWAT outfits
Veracruz Immigration: 229 989 7250 - Ext. 32804 Corner of Cinco de Mayo & Lerdo in Veracruz

Groceries:
24 hour mini grocery/liquor store:  knock on window at corner store at Madero & Democracia, one
block from Malecon, SW end of town.
24 hour restaurant: Loncheria Mingo, near plaza
Supermarket: Mini Aurrera at Catemaco entrance, 2 larger ones in San Andrés, Aurrera and Soriana
Grocery Stores: largest is El Rodeo, or the central market
Butcher shops: dozens, recommend San Miguel on Carranza

Cars:
Auto Parts: near the so called  "Y griega", exit to Montepio. VERY INADEQUATE.
Tires - Repair: several on highway
Tires - New:  highway in San Andrés Tuxtla
Gas Stations: 3 in Catemaco, on the coast near La Nueva Victoria
Mechanics: dozens, none recommended, San Andrés has service for Ford, VW, Nissan, Chevy, Chrysler
Locksmith: 2 blocks off Malecon, on Calle Corregidora in motorcycle repair shop
Car Wash: 2 blocks from Plaza, Calle Aldana, near Ocampo, opens at 9:30, charges 25 pesos
Tow Truck: Gruas 911, San Andrés,

Money and Banks:
Bank: only one Bancomer, on central plaza, exchanges dollars only till 2 pm, with passport.
ATMs: at Bancomer, 1 more on side of Municipal Palace, other in drugstore on the plaza.

Mail & Packages:
Post Office: Cuauhtémoc, almost corner of Reforma.
Package Service: Multipack at ADO bus station, more in San Andrés
Package Delivery: Post Office, UPS, Fedex, DHL deliver

Legal:
Notary:  there are 9 in San Andres Tuxtla, recommend Lic. Raul Mateu Sedas 294 942 1706
Lawyer - there are hundreds, recommend Lic. Jaime Fernandez 294 942 4270 in San Andrés Tuxtla

Others:
Barbershop: there are dozens, recommend El Cisne, 1 1/12 blocks from plaza on Carranza, 20 pesos.
Beauty Salon: many, recommend Shami, on Cuauhtemoc.
Phone Service: Telmex, office in San Andrés.
Cellular: dozens, to buy I recommend an analog phone, has more coverage in Mexico.
Funeral Homes: don´t die in Catemaco.
Cremation Service: in Veracruz city.
Laundry: several hotels have self service machines, but none in the city, drop off service only.

For more details:
Read the Catemaco Survival Guide
In case of an emergency...