int deckSize = deck.Count;

// show the last 5 cards in order
for (int i = 0; i < 5; i++)
{
    var drawnPage = deck[deckSize - 1 - i]; // shift by i each time

    buttonSlots[i].GetComponent<PageInHandButtonScript>().setPage(drawnPage);
    buttonSlots[i].GetComponent<UnityEngine.UI.Image>().sprite = drawnPage.getSprite();

    Debug.Log($"Page added to hand: {drawnPage.element} rune");
}

// now remove those 5 cards from the deck
deck.RemoveRange(deckSize - 5, 5);

Debug.Log($"Filled up hand. New Deck size: {deck.Count}");