The Gemoro in Brochos 35a says:
"אמר רב יהודה אמר שמואל כל הנהנה מן העוה"ז בלא ברכה כאילו נהנה מקדשי
שמים שנא' 'לה' הארץ ומלואה'. ר' לוי רמי: כתיב, 'לה' הארץ ומלואה',
וכתיב 'השמים שמים לה' והארץ נתן לבני אדם'? לא קשיא; כאן קודם ברכה, כאן
Rav Yehuda says in the name of Shmuel, “anyone who benefits from this world without first making a blessing, it's as if he he has benefit from the “holy things of heaven” ( = sacrifices (?) without permission) as it says, “The earth and the fullness thereof belong to Hashem”.
Rebbi Levi contrasted two verses: it says, “The earth and the fullness thereof belong to Hashem”(1) and it says “the heavens are heavens of Hashem, but the earth he gave to humans”(2). There's no contradiction – one is before he makes a blessing =(1) and the other is after he makes a blessing =(2).
So we can think that a blessing before food acknowledges that everything belongs to Hashem and that by acknowledging Him and thanking Him, He gives us permission to enjoy that item.
For the other categories of blessings, described by @Cashcow, the central feature is to acknowledge and thank Hashem.