They'll be more than fine for three days, and better to leave them unfed for three days (or even a week or two when going away) than to try using one of those autofeeders, "holiday blocks", or even having someone else feed the tank who doesn't know how much to give, and is likely to overfeed and not know how to fix it if they accidentally cause an ammonia spike by dumping too much food in.
Remember that fish are cold blooded, not mammals like we are. What this means relative to this, is that they don't generate their own internal body heat the way mammals need to, which requires a lot of fuel, and is energy demanding. Fish take their body temperature from the water they are in. So despite constantly acting hungry, they can actually be fasted for quite a while with no ill effects, and really don't need the daily or twice daily feedings most of us give them.
They are opportunistic feeders though, grabbing insects or whatever food when it becomes available, since they don't know when it may become available again, hence them constantly acting as if they're starving anytime you go near the tank. But they will be absolutely fine for 3-4 days while you're away! Our tendency to over feed our fish means a lot of us have days where we fast the fish, only feeding 4- 6 times per week instead of twice daily. Of course that varies depending on the fish you keep, the keeper's wishes, whether there are fry, which need more frequent and careful feeding, etc etc.
But for your average community tank with adult fish, a week or two is fine while you're away. They'll snack on whatever algae and microcritters they find in the tank while you're gone (worth leaving the glass uncleaned and allowing some algae and biofilm to grow for them to feed on, I only ever clean the front pane and maybe a side pane if it's also a viewing side, but the back and other side I leave algae to grow on for my algae eaters and shrimp). But just means you come home to a cleaner tank.
Hope you don't mind my asking, but looks as if you have the one neon, and two guppies?