There is nothing that spoils a vacation like loss of valuables.
Here are some basic tips to keep your valuables safe during a trip. So that you can focus on what you came for; Having Fun.
Warning: Thieves will hate you for this
1) Be picky about what you bring
The fewer stuff you carry, the lesser you chance of loss, and the more peace of mind you'll have.
Especially with beach vacations and adventure trips etc., the chances of losing stuff (mostly jewelry) is higher. Better leave them at home.
2) Avoid loose fitting stuff
Pickpockets love loose fitting clothes, jewelry, and bags.
The tighter your stuff is, the closer they stay to your body, and the harder they are to steal.
3) Carry your stuff in front of your body
Sling bags and money belts are your best friends here. They keep your valuables right in front of you, within view at all times.
Money Belts specifically can be worn under your clothing (hence difficult for pickpockets to access)
Back-pockets are very easy to pickpocket. Avoid keeping valuables here.
4) Split your stash
Store your cash, cards etc in separate places (carry-on bag, hotel-safe, check-in bag etc).
Even if you lose one, the others will back you up.
5) Use ATMs inside the bank
Especially in most western countries, most ATMs are not situated within a closed space.
Whenever possible, use ATMs inside the bank to stay safe.
6) Never leave you credit cards out of your sight
Make sure they swipe the card on the machine in front of you. No handing it over to service personnel for taking it backdoor.
7) Pick an accommodation that has a Safety Locker.
Leave a good part of your money and your passport in the locker.
Only carry what you need for the day, and a copy of your passport when you embark on day trips.
8) Choose a room that is not on the ground floor.
Rooms on the ground floor are most easy to break into. Pick a high floor to stay safer.
9) Carry a padlock with you
Whether for the hostel locker, or for your check-in bags, it is always a good idea to have a pad lock (numbered ones are better as you don't need a key) on you.
10) Be wary of people who are extra helpful for no reason
Yes you do come across super-helpful people during your travels. But this is the exception, not the norm.
Kind strangers are very rare. Be wary of them.
Further, do read up on the scams that are popular in your destination, and be prepared.
11) Give our minimum information
Scamsters are thieves are always looking to learn more about you to identify your weak points.
Do not divluge details of where you stay, who you are with, whether you are travelling alone etc. to people you meet on the road.
Share information only on a need to know basis.
Here is to a super safe vacation filled with fun and frolic.
Smooth Travels !