Moving fish to new tank

I've got the new 50 gal filled, the filter running, and am waiting for the
temp to come up. I put in the castle and troll and some of the glass marbles
from the 10 gal tank, and threw in the old filter (rinsed the gross big
stuff off with a little cold, non-chlorinated well water but that's it) I
don't have any plants to move to it at the moment- there was a recent
feeding frenzy. (why do they ignore the plants for days or weeks, and then
suddenly go nuts for them????)

When the temp comes up, I plan to move one fish over. Now, I doubt I can set
the heater accurately enough to get the two tanks perfectly matched, so I
figure on putting the 'test fish' in a bag and doing the "float the bag in
the new tank and slowly add the new tank water" routine, like I'd brought a
new fish home. Which leads to the question that is the whole point of this
post - is there something special about the bags the fish store uses? Or,
since I'll be sitting here watching it the whole time, thus limiting the
chance of the fish getting into a corner, can I use a clean new food baggie?
Or should I stop by and bum four fish bags from the LFS?
Thanks,

--
Laurie, Dark Phoenix

"Every dog has it's day, but nights are reserved for cats." -