On the grapes - as I said, seeds take longer to grow than saplings. Noach probably fully understood in what mental state he will be in when he exits the ark: In deep, deep depression: His whole world destroyed. Nearly all of his relatives and all of his friends - dead. Evidently, Noach wanted to be able to drown his sorrows ASAP. Hence, the need to be able to prepare wine ASAP.
On the figs, a fascinating idea is brought by Rabbi Yishai Zargeri in his book "Bigdei Yesha", pg. 67-68 (my translation):
"And it seems to me that the explanation is that we find that Noach prepared sacrifices when he exited the ark, and to light the fire he needed wood, and since all of the trees were soaked with water it wasn't relevant to light the fire from them, and so Noach needed to bring with him trees into the ark.
And it says in the mishna in masechet Tamid (pg. 29a) that wood from all the trees were fit for the arrangement to prepare upon them sacrifices, except for wood from the vine and from the olive tree, and if so, then Noach could not have used the grapevine branches that he brought with him, and he needed wood from a different tree, and then it says that though all woods were fit for the arrangement, but the priests were accustomed to assemble the arrangement with wood from these trees: With young branches of the fig tree, and it seems that they were the best in quality for burning, or for some other such reason, and per this we must say that for this reason Noach preferred to bring these trees into the ark to sacrifice upon them his sacrifice when he exited [the ark]."
