Vinegar eels are a possibility. Disclaimer: this about as small a live food you can get but very, very easy. May be suitable for CPDs and smaller(definitely a great fry food!!). 50/50 water/apple cider vinegar per volume of container. Add starter culture and poof.. nearly unlimited eels. I keep several cultures in small plastic Gerber baby food containers. Sealed except to feed to fishes. I literally have not changed media or, added to these cultures in almost six months. When I say small I mean small, I think the biggest one I've seen in my cultures is 1mm. Supposedly they can get up to 2mm. Also, mosquito larvae is very easy but, YOU have to be responsible with your culture and not let them molt into adults. If you go that route I strongly urge you to maintain a few cultures and monitor their growth stages. There are lots of gov't websites you can find information on mosquito life cycles.
Stock lightly and carry a big filter. - I don't have aquariums. I have ecosystems in a glass box. - Hygrophilaholic and hoarder of Anubias.