You're going to eat out. Planning for it beats pretending it won't happen and then treating it as a write-off. A restaurant meal is just another slot — usually a larger one, which the rest of the day can be built around.
Order first, before the table talks you into sharing the fried starter. Pick a protein you actually want. Add a vegetable or salad. Add one starch the size of your cupped hand, and ask to skip the second one if the plate comes with two.
Ask for sauces and dressings on the side — not to avoid them, but so you decide the amount. Grilled, roasted, baked, or seared instead of fried. Double vegetables instead of a second side of fries costs nothing to request.
Most entrées are two portions. Decide up front that half is coming home, and box it before you start if that's easier. On a GLP-1, an appetiser plus a side salad is often the right size for a whole meal — order it that way without apology.