This is just a bagatelle, but interesting nonetheless.
A friend told me that his father always used celery for Karpas, and he strongly dislikes celery. There are two reasons for this strong dislike. One, because celery is not a barbecued rib. Two, it is celery. He is already dreading the Seder because of the inexorable approach of the celery. So he asked, can he use a different vegetable?
I answered him that yes, he can use anything upon which you make a borei peri ha'adama. If he likes to dip Terra Chips into saltwater, he can use Terra Chips. He can use a banana, he can use pineapple. (Some poskim say that you make ha'adama on Papaya too because the stem is relatively soft and hollow. I strongly disagree. It can grow twenty feet tall and lives for years, and there are no early sources that consider the quality of the stem/trunk to be a factor. But if you follow Harav Ovadiah and not me, you can use a papaya, too. For an excellent discussion of the bracha on Papaya and the issue of Orla, this article from the OU.)
But his question reminded me of a story with the Chasam Sofer.
After stealing the Afikoman, the Chasam Sofer's son, later known as the Ksav Sofer, asked his father, why do we do this? Why do we steal the Afikoman? His father said nothing. He asked again; again no response. He realized that his father was not going to answer the question, and he did not ask again.
The following night, the Chasam Sofer told him, now I will answer your question.
The reason we steal the Afikoman is because it says by yetzias Mitzrayim "ולכל בני ישראל לא יחרץ כלב לשונו " Not a dog will bark at any of the Israelites, at man or beast ....
The Gemara (Psachim 113a) says
לא תדור במתא דלא צניף בה סוסיא ולא נבח בה כלבא
Do not dwell in a city where no horses neigh nor dogs bark.
and Rashi explains
סוסיא - משום דהוא נטירותא בקרתא מאויבים ומגנבים:
Horses: because (by reacting audibly to strangers) they provide safety from enemies and thieves.
So we see that dogs are a shmira from ganovim. That means that when the dogs are not barking, ganovim can do whatever they want. That being the case, by Yetzias Mitzrayim, ולכל בני ישראל לא יחרץ כלב לשונו, nothing would be safe from Jewish Ganovim. To commemorate that miracle, we steal the afikoman.
Why didn't I tell you this answer yesterday? Because you need to know that the first rule is to respect minhagim, even if you have no idea why the minhag makes sense. You do it with full faith. After you learn to defer to and properly respect minhagim, then I can tell you the reason for the minhag.
(I suspect that the question had been asked dismissively, implying that it was a foolish minhag, and the Chasam Sofer needed to correct this attitude.)
Back to Karpas. If you really dislike celery, you're welcome to use whatever you want. There is some benefit to doing precisely what your father did at the Seder. But the truth is, there are minhagim and there are minhagim. I think the choice of vegetable for Karpas is really not important, and you can choose whatever you enjoy. And if you choose to dip a banana into saltwater, instead of the mundane celery or potato, you can be sure that you are going to get questions from the younger members of the family - and that is exactly what you are trying to do!
I mentioned 'bananas' because I thought the image of using bananas for karpas was comical. It was that or strawberries in pink Himalayan saltwater. If you do want to go with bananas, I recommend banana chips.
But, in a cosmic coincidence, Reb Sass tells me that he heard that Harav Pinchas Teitz of Elizabeth davka used bananas for Karpas. He did so to publicize the fact that the proper bracha on bananas is indeed ha'adama, and by using them for Karpas, the word would get out. How do you like that?
I just got an email from eidim ne'emanim that Rav Teitz did indeed use a banana. It was not his innovation, though. It was the idea of his father in law, Rav Elazar Mayer Preil z’l, and Harav Teitz decided it was a good idea, and adopted it. I even got advice on how to do it like the Teitzes: Bring the banana to the table whole, and peel and slice it right before dipping, so it does not oxidize.
Reb Tzvi was kind enough to direct our attention to the shitta of my uncle, Reb Dovid Feinstein zatzal. I saw it in the Artscroll "Laws of the Seder" that he authored. Notable points there on page 35:
1. That the optimal mitzva is to use a vegetable that grows above ground, in that a root is not called a yerek. This excludes potatoes and carrots.
2. A fruit, even if you make ha'adama on it, would not be called a yerek, and, as such, is not lechatchila for Karpas. This excludes cucumbers and tomatoes.
3. That Karpas should be raw, not cooked, because according to some the Karpas should stimulate the appetite, and according to the first teretz in Tos Eiruvin 55b, only raw vegetables do that, while cooked vegetables satiate. This would exclude cooked potatoes.
4. That since onions are rarely eaten raw in the US, the bracha on onions is here and now shehakol.
HOWEVER, my father in law, as did his father, uses cooked potatoes and Reb Aharon used raw onions. Since I grew up using potatoes, and I married into the Reb Reuven side of the family, I feel comfortable recommending banana chips and strawberries.
NOTE: My wife reminded me that my father in law, out of respect for his brother, has been using both celery and potatoes ever since Reb Dovid publicized his opinion. Guess what we're having alongside potatoes this year.
IF you want to be really serious about your karpas - more serious than, for example, the Chofetz Chaim, then maybe you should do what many yekkes do, and use Parsley. As Reb Dovid points out, the Gemara never uses the word Karpas in the context of the seder, only Yerek. But since we call it karpas, the fact is that the Rishonim in other places generally say that Karpas is parsley. See Rav and Yachin on Mishna Sheviis 9:1, Rashi Sukka 39b. Some say that it is cress or celery. Parsley, if you can get it without insects, is perfect almost lechol hadei'os. I personally do not understand why you make a haadama on it - for men, it's a garnish, not a food, but I am alone in that opinion.