shabbat - eating before kiddush

Is there any time in the early morning on Shabbat in which I can eat and drink something without any question of it being considered eating before davening and kiddush? For example, at 3, 4, or 5 o'clock in the morning? Is there a certain time before netz or alot hashachar in which it's definitely acceptable to eat and drink on Shabbat morning? Also, does the type of food matter? As a second point, what if I wake up early during a weekday? Is there a point at which I can definitely eat and it's not considered eating before davening? is there a point I cannot begin to eat unless I first daven? Is there ever a time at which I'd have to stop eating and drinking and wait until it's time to daven to eat or drink again? Thank you so much for your help.