I need the rope from the honeymoon suite, but I already left the room before I realized I needed it. Whenever I try to go back in, Larry just knocks and there's no answer. Is there a way to get back in that I'm overlooking, or do I have to reload a save?

Blueskirt42 is correct. You have to reload a previous save game.

While we're at it, after you're done gambling back enough money to continue on (get yourself another $200 or so to be safe) be sure to purchase an apple. Wait outside the casino for a little bit, and somebody will come along selling apples. As far as I know, the only other dead end you'll have to worry about when you get beyond this point, besides running out of money, is if you don't have the apple when you need it.

Thank you both. Indeed there seems to be no way around my oversight, so I simply went back to an earlier save. Mercifully, this isn't a long or difficult game, so it was easier to redo than I realized. But good to know another potential way to get stuck, I suppose.

If you move onto Leisure Suit Larry 2, that game is longer, harder, and has A LOT of dead ends. Be sure to save a lot in that game and use multiple save slots every time.