A light and sponge filter would be nice!
To setup a sponge filter you need an air pump: https://smile.amazon.com/Tetra-Whisper-Easy-Aquariums-Non-UL/dp/B0009YJ4N6/ref=sr_1_6?crid=1AR81YYWFJ7TQ&keywords=aquarium+air+pump&qid=1579189396&sprefix=aquarium+air+%2Caps%2C182&sr=8-6
There are some really cheap sponge filter options, and they work just fine, but I like how this one has 2 sponges and 2 ceramic ball media areas, I just clean 1 of the 4 "zones" each week when changing water (rinse the sponge or ceramic balls in old aquarium water): https://smile.amazon.com/Aquaneat-Sponge-Aquarium-Ceramic-Airline/dp/B07SFCRGG6/ref=sr_1_15?keywords=sponge+filter&qid=1579189516&sr=8-15
Nice little light with day and night settings: https://smile.amazon.com/ECtENX-Aquarium-Light-Lighting-Color/dp/B07FNDPG4L/ref=sr_1_6?keywords=beta%2Blight&qid=1579189718&sr=8-6&th=1
Edit: Also, betas like the water about 78 deg F, so you might want a heater: https://smile.amazon.com/Aqueon-100106251-Preset-Heater-50W/dp/B00Q78MMT6/ref=sr_1_3?keywords=5gal+heater&qid=1579189843&sr=8-3
so something like this: http://www.amazon.com/Tetra-77851-Whisper-Pump-10-Gallon/dp/B0009YJ4N6/ref=sr_1_1?s=pet-supplies&ie=UTF8&qid=1404519448&sr=1-1&keywords=air+pump
might be everything i need?