Can’t be summoned on Old Iron King

Using a Token of Fidelity while in another players world allows you to heal the host of the world. Having Token of Fidelity in your inventory is also required in order to join the Blue Sentinels covenant.

Having Tokens of Spite in your inventory increases your chances of getting invaded.

The trick is to raise your fire-resistance stat. The minimum is at about >600 to be able to reach any item (you'll get the item, but you will die).

Raising it to >1000 is recommended.

Note: You'll still take damage, but not as fast. Be quick and you should get the items. It's also recommended that you spend your souls before you attempt a run on the items.

You can raise your fire resistance with certain armour, rings (Flame quartz ring), the pyromancy flash sweat (gives +300) and items (orange burr but doesn't stack with flash sweat).

There are also 2 Pharros' Contraption that, when activated, spill water into a pool in front of them. When you roll in the water, you temporarily boost your fire resistance by +400.

Additionally, there are huge vases scattered through the level that contain water, which have the same effect as the water from the Pharros' Contraption. Just roll through them.

To get the item (the iron key) from the fire-breathing trap, you can either carefully inch your way to it, till you get the pick-up prompt or you can deactivate the fire with a switch, later in the level.

Source: Darksouls 2 Wiki