use substitutes - such as pasta for noodle

当然也就是简单的中餐了.面条什么的.
至少要买写蔬菜和水果呀..这些不能带去吧.

Vegie and fruits should be available in the convenient stores at hotel zone - both in the mall, or in the few areas where the shops/restaurants concentrated (where the road becomes a fork for opposite direction - about 2/3 from the south end of hotel zone, and 1/3 from town).

还有个重要的问题:带多少CASH呢?可以用CREDIT CARD吗？
需要兑换当地的ＭＯＮＥＹ吗？如果是，方便吗

Cash depends on your daily expenditure. Of course you can use CC - just bear in mind, your CC will charge you 3% foreign currency conversion fee, it would show up as a one-line entry on your monthly statement when you have charges in foreign currency. There are some cards only charge 1% but most major cards charge 3% - just chalk it up as part of your travel expenses.

You would be better off to use some Peso - either exchange your USD cash at the local exchangers - they are all over the places, in the Mall and on the streets - and the rates are all different - you need to know the prevailing xchange rate and make sure only use the exchanger whose rate, together with service fees, are not outrageously higher than the prevailing rate.
Here is a link to check exchange rate:

http://www.xe.com/ucc/

Bear in mind, the rates posted there are the MultiMillion $ interbank rate - you will NOT get such rate, would be slightly worse.

The other method is to use ATM - again, it depends on which bank you have your account - most banks charge a hefty International withdrawal fee per each withdrawal - $5 or more, AND some banks also charge 1% to 3% foreign currency conversion fee.
If your bank is BofA - they have a network member bank in Mexico and you can avoid withdrawal fee by only getting your cash from the ATM of the member bank - forgot the name of it you can google yourself.
Citi owns Banamexico, so if your bank is Citi, get money from Banamexico ATMs also wont incur withdrawal fee.

I hate to say it, but judged by the questions you asked so far, you are not well-prepared for a trip aboard, let alone to a destination like Cancun. Hope you can overcome the challenges and still have a good time.