Regarding the use of dumbbells or elastic bands, I'd just use whichever you have.  The whole key to exercise is just to stick with it, consistantly, day in and day out.  It is so easy to get distracted, to believe you can't exercise today because you don't have this or that equipment.  I'm guilty of that myself, and I have spent (wasted) alot of money over the years on exercise stuff that basically sits unused too much of the time.  It's maddening!!  So my advice would be for you to use what you have right now.

Also, I'd feel guilty too about just drifting around to different gyms and using them only as long as they're free.  It really isn't right in my opinion, plus it's alot of effort to keep juggling!!    I also think I'd be more inclined to go regularly if I actually paid for the use--I always want to get my money's worth.  I think it would be very very easy to say "nah, not going today" if there was no money involved. 

Keep at it Boston!!!

To play devils advocate for a second i dont think your friend is soing anything wrong by going to the other gyms just for the free trial as long as her going is causing someone who wants to go and sign up for a membership to not get in.Businesses give away free trials and time knowing that not everybody is going to sign up or buy their products. So if i was doing it I would not feel guilty, unless I am taking the trainers time away from someone who is there for it.