You are going to travel so make sure you know when to plan what. This seems to be obvious and yet you find people running around trying to get a last minute visa or suddenly grandma announces she does not have a passport. Important things that may take time so see what they are and just get them done Visa Bookings.
Flight Arrangements
Get your flight ticket ahead of time. While you can use a stand by ticket this might not be a good thing if you have children or elderly people with you.
Passports:  You forgot to apply for what?
You will be surprised to know that one of the things the first Space travelers had was a set of passports. Early space flight was planned exceptionally well, but there was the chance that a capsule would enter the atmosphere and drift into a foreign country. They could then show their passports to a farmer who might have never heard of America. If this rule is still followed I am not sure.
Look at the following:
1. Make sure you have a passport
2. When does it expire?
3. Will it expire while you are on holiday?
4. Can you travel on a temporary passport?
5. Get a passport long before you need one.
6. Before you go make sure you have spare pages especially if you will visit different countries.
Visas: You need your visa when?
Find out if you need to have a visa. Sometimes you can get a visa on the border. Do not go to Mozambique from South Africa only to find you need to go back 400km because you need to apply in Pretoria. Do not assume anything when you need a visa. While a visa application can be handled in hours, some demand you apply a week in advance. Check the internet for the correct period, and office.
Super Tip: Certain countries demand you hand in your application before a certain time in the morning. Do not think you can slip in at the last second. Trust me I have had to turn around and come back the next day. While the person behind the glass will look at you and listen to your sad story they have a right to refuse your application. They often do. 
 Currency Exchange:  You want to pay with what?
Get your traveler checks by arranging it with the bank ahead of time. You may exchange money into a different currency on the airport but make sure you have enough to last until you can exchange more money at a hotel or other convenient places. Convert your money at banks whenever possible as they give better rates than hotels, travel agencies, exchange booths and tourist offices.  It is more expensive to purchase the currency in your own country than it is once you have reached your destination.
Health:  You really need all these pills?
Follow the rules because if you entered or will enter certain countries you need to prove you have taken the prescribed medication or had the injections. Arrange health insurance and if you have a chronic illness talk to your doctor for help. Get the medication for your epilepsy, heart condition and wear your Medic Alert Identification Tag. Keep the medication in the original labeled vials.
While you make think it is so obvious that certain things should be done it is also the reason why nobody ordered the wedding cake, why the bridegroom is without a suit. List them just to make sure you have them because if you forget you will not always be able to rectify the problem. Certainly not today.