I wouldn't recommend it. I might get a bit of flak for this...but if you really, really want a piece of chocolate cake, have a piece of chocolate cake. If, that is, it won't trigger a diet meltdown. I'd suggest you check out
www.glycemicindex.com. SouthBeach is basically a low-GI diet. Anthing with a glycemic index of 50 or below is considered low-GI. Of course, the other emphasis is on what bodybuilders call "eating clean", that is to say eating things with few additives and of course not many refined grains. Which is to say, just because chocolate cake has a GI of 38 doesn't mean you should eat it every day, or even every week! But IMO an important part of any WOE is to be able to indulge yourself occasionally without guilt. If you have one slice of cake in the course of, say, a month, it is probably not going to derail your diet or even stall your weightloss. Of course, everyone is different. Some people have to avoid bread altogether because it acts as a trigger for other cravings.
As far as ice cream & peanut butter go...Ice cream in general is forbidden on Phase Two, but NSA Fudgsicles are OK as early as Phase One, so use your common sense there. You'd probably be OK with NSA ice cream on occasion, but there's no need to buy carb-controlled ice cream. Check the carb counts on the carb-controlled stuff versus the sugar-free stuff, I doubt you'll find much of a difference. The main difference is going to be in price!
Peanut butter is OK in Phase One too, so why buy the carb-controlled stuff? Honestly, if you buy natural peanut butter, what it has in it is peanuts & salt. There's no way to take carbs out of peanuts! Natural peanut butter is very yummy too. You just have to stir before eating. :lol
The marinades...I don't know. It's another case where I'd suggest reviewing the ingredients on the normal stuff. If there's not added starches & sugars in the marinades, they're probably OK as is. I know low-sugar commercial dressings are OK in Phase One, & Wishbone makes a citrus vinaigrette with 4 g of sugar a serving that is
excellent as a marinade. Generally, though, it'd probably be cheaper & easier to make your own.
I hope I had something in there you'd find helpful.

One last thing: media reports aside, South Beach is
not a low-carb diet. It is a
good-carb diet. I'm sure you'd make the people who market those specialty foods very happy by buying them, but by & large there's no reason to.