What's in season depends on when you're going : )
I haven't actually fished it but I think it's basically a bass fishery (smallmouth?) and that opens the 4th saturday in June. If you're going sooner than that, I dunno, there might be panfish you can target, and some of the lakes in the area have pike. Certainly Spider Lake does and perhaps Westphal. And Georgian Bay is only 2 portages away and could have all kinds of fish.
I don't mean to say you shouldn't put stock in sk8r's opinion by the way, I'm no great expert in the area. I've gone Three Legged to Creswicke once, and much longer ago I went Three Legged to Gooseneck Bay which is a similar route. I didn't have wind problems either time but I suppose that's just luck. When I went to Creswicke it was as a two-day loop, returning the long way via Georgian Bay and Canoe Lake. I think at one point I lost a portage trail, but I think it was west of Creswicke, and only because I had the canoe blocking my view.
Not sure what to say about day trips... in terms of following real routes your choices are backtracking into the lakes you came in on, or continuing west which would soon put you among cottages in Georgian Bay. If there are any interesting bushwhacks or anything in the area someone else will have to reveal them.
Rather than looking at Google Maps, you can measure actual distances using the provincial government's topo mapping tool:
http://www.giscoeapp.lrc.gov.on.ca/matm ... cale=en-US You'll have to refer to the park map for portage locations if you want to be exact, though.