Gladiolus is all about survival and his skill reflects this, as he will gather items after battling with enemies. Note that you need to kill all of the enemies in order to get an item after a battle, so if you run away in the middle, then you won't get anything. Gladio's Survival skill is leveled up by just running around with Noctis, not riding a Chocobo and not riding around in the Regalia. This is the longest skill to level up, so it's very important to forgo the transportation when you can and just journey on foot.
The items that Gladio picks up depends entirely on the level of his skill, with each level adding new items and also increasing the chances of getting some of the rarer pieces. Note that the probability of finding an item during a battle depends entirely on the number of steps taken after last getting an item. So, the more time and space you travel on foot between battles, the higher the chance you'll have to get an item after the battle.
|1||Potion, Fossil Shell, Beetle Shell, Antidote|
|2||Potion, Antidote, Fossil Shell, Beetle Shell, Remedy|
|3||Potion, Hi-Potion, Remedy, Fossil Shell, Beetle Shell, Rare Coin, Antidote|
|4||Hi-Potion, Ether, Remedy, Beetle Shell, Debased Silverpiece, Rare Coin, Antidote, Fossil Shell|
|5||Hi-Potion, Ether, Elixir, Beetle Shell, Rare Coin, Debased Silverpiece, Remedy|
|6||Hi-Potion, Elixir, Hi-Elixir, Rare Coin, Debased Banknote, Remedy, Ether, Glass Gemstone, Beetle Shell|
|7||Elixir, Hi-Elixir, Phoenix Down, Glass Gemstone, Rare Coin, Debased Banknote, Hi-Potion, Ether, Beetle Shell|
|8||Mega-Potion, Phoenix Down, Hi-Elixir, Glass Gemstone, Rare Coin, Debased Banknote, Elixir, Beetle Shell, Megalixir|
|9||Phoenix Down, Mega-Potion, Hi-Elixir, Glass Gemstone, Rare Coin, Debased Banknote, Elixir, Beetle Shell, Megalixir|
|10||Phoenix Down, Hi-Elixir, Mega-Potion, Rare Coin, Debased Banknote, Elixir, Glass Gemstone, Platinum Ingot, Beetle Shell, Megalixir|