If you go on a PvP server, the best idea is to use your sword with fire aspect enchantment, and your bow with flame. It won't always work (some people will have fire resistance on their armor), but it does work in many cases. You could also use sharpness on your sword and power on the bow.
TNT and flint and steel are usually disabled on PvP servers, but if they are not, they could be valuable.
Use lava or water to slow people down if they are chasing you.
Enchanted golden apples are also very important to keep you alive. They practically make you invincible.
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play minecraft.... he doesn't exist xD
Get someone to give it to you. It's not technically "free", but it's free as far as you're concerned.
If you are looking for a easy way to install mods, someone made another Minecraft that can be used for downloading mods easier.
With a stone pick.
The only legal way to get "the real Minecraft" free is to have someone else buy it for you and give it to you.