How to I give a player a item every time they spawn? 1.13+

Here it is all the commands you'll need:

One time activation:

 /scoreboard objectives add death deathCount
 /scoreboard objectives add dummydeath dummy

Here it is the chain, connected to a Repeat command block:

/scoreboard players set @a[scores={death=1}] dummydeath 3
/scoreboard players set @a[scores={death=1}] death 0
/execute as @a[scores={dummydeath=1..},nbt=!{Inventory:[{id:"minecraft:carrot_on_a_stick",tag:{display:{Name:"[{\"text\":\"Dash Attack\"}]"},Enchantments:[{id:"binding_curse",lvl:1},{id:"vanishing_curse",lvl:1}]}}]}] run scoreboard players remove @s dummydeath 1
/execute as @a[scores={dummydeath=1..},nbt=!{Inventory:[{id:"minecraft:carrot_on_a_stick",tag:{display:{Name:"[{\"text\":\"Dash Attack\"}]"},Enchantments:[{id:"binding_curse",lvl:1},{id:"vanishing_curse",lvl:1}]}}]}] run give @s carrot_on_a_stick{display:{Name:"[{\"text\":\"Dash Attack\"}]"},Enchantments:[{id:"binding_curse",lvl:1},{id:"vanishing_curse",lvl:1}]} 1
/scoreboard players remove @a[scores={dummydeath=1}] dummydeath 1

So, the game works in an interesting way: When you die, you drop your items and, after clicking in the respawn button, the game will clear your inventory;
You can give items to dead players;

We can abuse this the following way:

• When a player dies, give them a score of 3 to dummydeath .
• If they don't have the Carrot on a stick, remove 1 from their dummydeath score.
• If they don't have the Carrot on a stick, give it to them.

(At this point, the player will be in the death screen with a carrot on a stick in their hands and with a dummy score of 2; Once they click respawn, they will have their inventory cleared)

• If they don't have the Carrot on a stick, again, remove 1 from their dummydeath score.
• If they don't have the Carrot on a stick, give it to them.
• Remove 1 score from dummydeath from every player that has 1 score of dummydeath

Interestingly enough, this can work for anything related to respawing players, if there wasn't already a solution to it.