I think this is ahead of time (by about 19.5 hours), but I'm going to post it now so there's some time for feedback.
Challenge: Complete the first three stages of Super Contra arcade version without dying; don't use the Shell (bomb item) in the top down stage (Stage 2). For extra bragging rights, you can take out all parts of bosses before defeating them, but it's not necessary.
(I was thinking about doing the full game, but that would take a bit longer because learning some of those enemies if you don't know the tricks takes a while, longer than I can reasonably expect most people to want to attempt in a week, although I feel that if you can beat the first three stages without dying you're very close to completing the full game on Normal. This is not as hard a game as its reputation suggests, at least not on Normal difficulty where you can cheat quite a bit. Hard mode is another story, that's got some epic difficulty.)
Rules: DIP switch settings are MAME defaults: Normal difficulty; lives and continues don't matter because you won't be dying (although it's perfectly alright to use Continues, or even savestates for practice only, if that helps you out). Either version in MAME is fine; the difference is that the Japan board has a better title screen and lets you play a harder second loop, whereas the game ends after beating the final boss in the US version.
Tips for victory:
You can upgrade your guns by picking up the same icon again. Some guns end up much better than others (lightning gun seems to do double damage, for example, but is still pretty useless). Picking up any weapon gives you invulnerability for a short period, but stages are predictable enough that it's not needed.
Your heroes can jump higher if you pull up on the joystick while jumping.
You can tap the fire button quickly (with two fingers) to fire the first level rapid fire gun very quickly. Also keep in mind that if you're playing with a keyboard and holding the fire button down that you may have trouble registering jumps - key priority issues. A wired controller isn't a must though; I've been playing with a keyboard.
Stage 1: The tank can be obnoxious if the machine gun fires right before a tank shell. You may be able to jump over it, but it's best to prevent the guns from firing in the first place.
At the boss, sometimes the second rapid fire gun icon disappears if it lands on the ground in a certain spot.
After defeating the helicopter, and you run to the bunker entrance on the right, beware of a green beret running up close behind you (from the left). He's almost always there.
Stage 2: This stage is no problem. The rapid fire gun, and probably others as well, can shoot farther than enemies can. Check out the blinking lights on the heads of the boss guys!
Stage 3: Be careful and watch for movement, especially trails of bullets. Just like Super C you'll be firing into the trees a lot. It may be worthwhile to inch along and let unwanted powerup blimps fly away so you don't have to worry about unintentional pickups.
The boss is hardest if you try to take out the little goo spitting cherubs (okay they're about as close to a cherub as a housecat is to a spider, and about as pretty as that thing from Sengoku Ace). Thankfully, you don't need to. I think they give some ridiculously low point value (like 1000 points each, if that) for how difficult it is to destroy them when compared to the bosses' point payout (something like 100K), how much longer it lives, and how difficult its attacks are to dodge when you go after them.