When a guitarist buys his first guitar he always gets also a pick and mostly this will be the brand he uses for the rest of his life while pedals, guitars, amps and speaker will be modified or changed frequently.
But also a pick can be decisive for the sound. The material and also the thickness of a pick can affect on the sound.
Brian May or also the guitarist of ZZ Top use a coin as a pick. The Edge of U2 always uses the rough backside of his pick which actually should provide a better grip.
When I by hazard got a Dunlop Ultex Sharp I recognized for the first time that my guitar sounded somehow more fresh and lively.
And the following anecdote showed me that this was not only my subjective feeling: one day another guitarist came to me to try one of my guitars that he wanted to buy. But while he tested the guitar he confessed that to him the sound of the guitar seems some kind of muffled. I gave to him a Dunlop Ultex Sharp and he was really impressed by the difference of the sound. Finally he did not buy the guitar but he took the pick with him.
The advantage of pick is that they are pretty cheap and you can get a large selection to try different kinds.
I for example use the pick of a certain brand in three different thicknesses because they create a varying sound depending on their thickness. The thin pick is able to clear up the sound of a Les Paul while a thicker one makes the Telecaster sound a bit more voluminous.