Nepenthes of any kind isn't a good idea, being undrained you'd be taking a pretty big risk of root rot. Additionally, nearly any nep besides possibly argentii would outgrow that sooner or later, and with the small opening you wouldn't be able to divide or trim them very easily, if at all. VFT, Sarrs, and temperate drosera and pings are right out for obvious reasons. Helis, even if acclimated, and imo most other drosera wouldn't work well due to light requirements. Cephs might could
theoretically work with a well-drained substrate to prevent root rot, but to me the lack of airflow means crown rot would be a pretty big concern, especially if the crown ever got any sort of moisture on it. I might miss a genus, but I'd also rule out Brocchinia and Drosophyllum due to size alone. I have no idea about Catopsis and Triantha, but neither are really terrarium plants anyway. Aquatic and semi-aquatic utricularia as well as Aldrovanda are also out due to algae growth in standing water, and would just look terrible before long anyway. All that being said:
- The first potentially viable option to come to mind might be terrestrial utricularia (sandersonii, calycifida, possibly longifolia might be some workable, visually appealing candidates). In a similar vein, I'd think Genlisea might also work. My concern, however, would be algae growth in such a high moisture environment and difficulty of maintenance in the event that became an issue.
- In light of the moisture issue, I can't think of a reason that some easier, preferably lower-light mexican pings couldn't work if you used a healthy layer of a very well-drained substrate (turface, pumice, sand, etc) and were careful with watering. I probably wouldn't try species that require a bone-dry dormancy such as gypsicola, but besides that I think most others could work. Additionally, they don't divide or spread on their own quickly enough to be much of a concern, and their flower stalks are short enough that it appears they probably wouldn't hit the top of the jug. You might could try a ceph here, but I wouldn't hold my breath for long-term success.
- Getting a little more out there, D. prolifera, adelae and potentially Andromeda might could work if you planted the adelae in a solid cup or used weed barrier or something to keep it from taking over, but prolifera would still spread via its runners meaning maintenance would still be periodically required. I don't grow Andromeda so I don't know how prone to spread it is but it would probably work otherwise, and schizandra is reportedly difficult even under proper conditions so it probably isn't worth trying here.
- A final fringe, and not technically carnivorous option might be Stylidium. I can't remember offhand about their exact care requirements, but S. debile has been a weed for me in a pretty sandy substrate and fairly low water level (I grow it in the same tray as my pings, though I keep them wetter than most do). The flower stalks, if they'd be short enough and you could get them to bloom, would probably be appealing in a terrarium setting.
All that said, of these 4 that I mentioned, I'd say pings are probably the most likely to succeed long-term with Stylidium as my runner-up.
EDIT: read 5 gallons instead of liters since I have a similar jug available to me I was thinking about a while back. Stylidium stays unchanged, utricularia would be limited to 1-2 short-flowered species like sandersonii and potentially calycifida, pings would probably be limited to smaller species like ehlersiae or gracilis or a few medium-sized like pirouette, and adelae is probably out since it'd need nearly constant plantlet removal but prolifera could still work.