There are a few ways to make money on the budgets specified. And i'll be specific on some points an highlight some realities.
1)You can still play card games for bitcoin. it may suit you since that is your skill. just make sure the site isn't a scam. Honestly with your expertise and focus, why change a good thing?
2.)The easiest investment that isn't holding is earning interest at some kind of exchange/ business/ or savings account.
Freebitco.in is an example of a mining business paying you interest for them to invest your bitcoin. Think grass roots market money account.
https://freebitco.in/?r=4783577 if you felt like helping me out here is a refferal link. (this site has a thread on this very forum and is trusted. I highly recommend it and personally have invested in it. PM if you would like my take on it.)
Another site is Bsave which initially teamed up with coinbase but is an independant operation now.
Both sites accrue interest daily. So the more you invest the more you get at a decent rate.
3.)You can lend bitcoin at various levels of risk and interest rates. the most unstable going up to the 15-20% range. But the initial investment for these sites are steep often at 1 bitcoin so a budget of $100's or even $1000's may not cut it.
This is the most lucrative more passive investment.
More Direct methods include:
1.)Holding and trading.
Buy as much as you can low and sell high. Recently a nice time to sell and wait was when the BTC price hit 5000. now you could get 1/5th more at it's current state if you were on the ball.
issues with this option are that you lose passive income opportunities and are truly gambling based on international factors and sound bites. This is an investment broker like situation and is the wild west.
I will say however. that this is often the fastest way to gain more bitcoin if you are on your toes.
2.) With hundreds you may be able to make an extremely sub par mining rig if you so desired.
In conclusion.
I'm in a similar budget constraint situation and am squeaking out small earnings that will grow over time. I'm currently making 5-10 cents a day passively with plans to constantly double this every few months. My second income is forming.