When you are going to spend your holiday in Bali an Indonesia visa should be obtained. This can be bought upon arrival for most of the nationalities.
Before customs you will find a small visa booth where you can pay for your visa in cash. A 30-day tourist visa costs $25 USD and $10 USD for 7-days.
Some nationalities do not need an Indonesia visa at all. Nationals from Chile, Malaysia, Philippines, Thailand, Peru, Macao, Morocco, Brunei, Hong Kong, Singapore and Vietnam don't need the 30-day visa for staying in Bali. They are issued a maximum 30-day visa free permit.
Nationals from these countries only have to show a valid passport with a validity of at least 6 months and a return or onward flight ticket. This visa free permit is not extendible or convertible if you are planning to stay longer than 30 days in Bali.

Indonesia visa on arrival at Ngurah Rai International Airport Bali
If you do intend to stay longer on this permit it will cost $20 USD a day within 60 days and after 60 days it will be 25.000.000 rupiah or 5 years in prison.
The following countries can buy a single entry-visa upon arrival at the 'Visa Indonesia booth': Argentina, Australia, Austria, Bahrain, Belgium, Brazil, Bulgaria, Cambodia, Canada, China, Cyprus, Denmark, Egypt, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, India, Iran, Ireland, Italy, Japan, Kuwait, Laos, Liechtenstein, Luxembourg, Maldives, Malta, Mexico, Monaco, Netherlands, New Zealand, Norway, Oman, Poland, Portugal, Qatar, Russia, Saudi Arabia, South Africa, South Korea, Spain, Surinam, Sweden, Switzerland, Taiwan Territory, United Arab Emirates, United Kingdom and the USA
Your passport has to have a validity of at least 6 months at the moment you arrive in Bali and you have completed your airline embarkation - disembarkation card. These Indonesia visas upon arrival are only valid for 30 days and not extendible or convertible into any other types of visas.
If you stay longer than the allowed 30 days with an Indonesia visa you're in trouble...
The Indonesian authorities handle your case the same way as the nationals that come into the country with a visa free permit.
Every day that you stay longer until 60 days will cost USD $20 and after these 60 days it will cost 25.000.000 rupiah or a 5 years prison sentence.
If your country is not in the above lists you'll need to arrange an Indonesia visa at the Indonesian consulate or Indonesian embassy in your country of residence before arriving in Bali.
Another thing you should be careful about is to bring illegal drugs into Indonesia. The Indonesian authorities are very serious about it since you are likely to receive the death penalty.

When you leave Bali the airport charges you the 'good-bye Bali' tax of 150.000 Indonesian rupiah.
This has to be paid in cash at the check-in counters so don't spend it on your last nasi goreng or souvenirs before you leave the island. When you take a domestic flight you'll pay 30.000 Indonesian rupiah.
Most of the airlines allow you to have 20kg check-in baggage and 8kg of hand luggage including laptop but when you fly with AirAsia they have a 15kg limit on check-in baggage and 7kg on hand luggage.
Pack light or be prepared to pay excess baggage per kilo.
I remember my grandmother having various unique shells from the Pacific and pieces of coral displayed in her house but those days are over.
It's prohibited to carry any sea shells, pieces of coral, souvenirs made from turtles or snakes such as handbags in your luggage.

Even when you stroll along the beautiful beaches in Bali and find some interesting pieces of coral don't put them in your luggage as cute Bali souvenirs. You will end up paying a huge fine when you arrive back home.
So don't be tempted to buy it, it's nicer to see it in the wild than to place it on a dusty shelf...