This should fix all errors related to regular crashing upon picking up food due to an index error. This uses a modulus to make the coordinates conform to the grid instead of a list.

python_Snake.py

import turtle as t
import random as r
import time
# Death delay
delay = 0.1
# Score
score = 0
high_score = 0
# Var defs
w = t.Screen()
p = t.Turtle()
x = -290
y = -290
# Screen setup
w.title("Snake")
w.bgcolor("White")
w.setup(width=600, height=700)
w.tracer(0)
p.speed(1)
p.hideturtle()
# Functions:
# funtion for grid modulizing
def gridModulo(n):
    return(n-(n%20))
# Function for grid lines
def vertical_line(x):
    p.penup()
    p.goto(x, 290)
    p.pendown()
    p.goto(x, -290)
def horizontal_line(y):
    p.penup()
    p.goto(-290, y)
    p.pendown()
    p.goto(290, y)
# Loop to make grid lines
while x < 300:
    vertical_line(x)
    x += 20
p.hideturtle()
while y < 300:
    horizontal_line(y)
    y += 20
# Snake movement & distance
def move():
    if head.direction == "up":
        y = head.ycor()
        head.sety(y + 20)
    if head.direction == "down":
        y = head.ycor()
        head.sety(y - 20)
    if head.direction == "left":
        x = head.xcor()
        head.setx(x - 20)
    if head.direction == "right":
        x = head.xcor()
        head.setx(x + 20)
# Functions for snake to go up down left right and not go back in on itself
def go_up():
    if head.direction != "down":
        head.direction = "up"
def go_down():
    if head.direction != "up":
        head.direction = "down"
def go_left():
    if head.direction != "right":
        head.direction = "left"
def go_right():
    if head.direction != "left":
        head.direction = "right"
def start_text():
    penstart.write("Press Any Arrow Key to Start", align="center", font=("arial", 24, "normal"))
    w.onkey(start, "Up" or "Down" or "Left" or "Right")
def start():
    penstart.clear()
def death():
    pendeath.write("Oh no! You died with a score of {}".format(score), align="center", font=("arial", 24, "normal"))
    if head.direction != "stop":
        pendeath.clear()
# Snake head config
head = t.Turtle()
head.speed(0)
head.shape("square")
head.color("green")
head.penup()
head.goto(0, 0)
head.direction = "stop"
# Food config
food = t.Turtle()
food.speed(0)
food.shape("circle")
food.color("red")
food.penup()
food.goto(x=gridModulo(r.randint(-240,240)),y=gridModulo(r.randint(-240,240)))
# Segment
segments = []
# Pen for score text
penscore = t.Turtle()
penscore.speed(0)
penscore.shape("square")
penscore.color("black")
penscore.penup()
penscore.hideturtle()
penscore.goto(0, 300)
penscore.write("Score: 0   High Score: 0", align="center", font=("arial", 24, "normal"))
# Pen for start text
penstart = t.Turtle()
penstart.speed(0)
penstart.shape("square")
penstart.color("black")
penstart.penup()
penstart.hideturtle()
penstart.goto(0, -325)
# Pen for death text
pendeath = t.Turtle()
pendeath.speed(0)
pendeath.shape("square")
pendeath.color("black")
pendeath.penup()
pendeath.hideturtle()
pendeath.goto(0, -325)
# Keyboard bindings
w.listen()
w.onkeypress(go_up, "Up")
w.onkeypress(go_down, "Down")
w.onkeypress(go_left, "Left")
w.onkeypress(go_right, "Right")
# Main game loop
while True:
    w.update()
    if head.direction == "stop":
        start_text()
    if head.direction != "stop":
        penstart.clear()
    # Check for collision with border
    if head.xcor() > 280 or head.xcor() < -280 or head.ycor() > 280 or head.ycor() < -280:
        time.sleep(1)
        head.goto(0, 0)
        death()
        time.sleep(2.3)
        head.direction = "stop"
        # Hide segments (body parts)
        for segment in segments:
            segment.goto(1000, 1000)
        # Post death segment reset
        segments.clear()
        # Post death score reset
        score = 0
        penscore.clear()
        penscore.write("Score: {}   High Score: {}".format(score, high_score), align="center", font=("arial", 24,'normal'))
    # Check for collision with food:
    if head.distance(food) < 20:
        # Move food randomly
        food.goto(x=gridModulo(r.randint(-240,240)),y=gridModulo(r.randint(-240,240)))
        # Add segment to body
        new_segment = t.Turtle()
        new_segment.speed(0)
        new_segment.shape("square")
        new_segment.color("light green")
        new_segment.penup()
        segments.append(new_segment)
        # Shorten delay to reduce lag appearance
        delay -= 0.001
        # Increase score
        score += 10
        # Update high score
        if score > high_score:
            high_score = score
        penscore.clear()
        penscore.write("Score: {}   High Score: {}".format(score, high_score), align="center", font=("arial", 24,'normal'))
    # Moving end segments
    for index in range(len(segments) - 1, 0, -1):
        x = segments[index - 1].xcor()
        y = segments[index - 1].ycor()
        segments[index].goto(x, y)
    # Move segment 0 to where the head is
    if len(segments) > 0:
        x = head.xcor()
        y = head.ycor()
        segments[0].goto(x, y)
    move()
    # Check for body collision
    for segment in segments:
        if segment.distance(head) < 20:
            time.sleep(1)
            head.goto(0, 0)
            death()
            head.direction = "stop"
            # Hide segments (body parts)
            for segment in segments:
                segment.goto(1000, 1000)
            # Post death segment reset
            segments.clear()
            # Post death score reset
            score = 0
            penscore.clear()
            penscore.write("Score: {}   High Score: {}".format(score, high_score), align="center", font=("arial", 24,'normal'))
    # Slows down whole program
    time.sleep(delay)
w.mainloop()