During the inbound flight, you will receive and need to fill out a customs form (Hacienda). After passing through immigration, you collect your bags and proceed to the exit. You will hand the form to the customs agent and press the button on what looks like a traffic light.
A green light means "go" and red means "inspection" in which case, officials perform a quick inspection.
As a rule of thumb you are allowed to bring into Mexico whatever you need for the time period you will be staying in Mexico. You are not allowed to bring food, fruits and/or products that are not "company" packed and sealed. And if you are bringing food or products they are allowed only if you need them because of a special diet or for medical reasons.
The same rule applies to medicine. You are allowed to bring enough medicine for the time period you will be in Mexico. If you are bringing an unusual quantity of medicine please bring a doctor's prescription just in case you need to prove the medicine is for your own consumption.
If you have any questions about Mexican Customs please check our FAQ section. There is a good chance somebody already asked that question. If not, then we strongly recommend you contact your nearest Mexican Consulate. There you can get more specific information about anything that has to do with "allowances" and what products are prohibited in Mexico. Here is a link to Mexican Consulates around the world:http://www.inm.gob.mx/index.php/page/Embajadas_Consulados