Another problem some users noted in the (now deleted) comments for this question is that a 2nd level party is not suitable to an adventure in a hellish plane, since, besides the hardness of obtain the basics of food and water in Hell, there are high level monsters and dangerous environmental hazards.
So, taking into account that you party has a goal to delve into hell in order to save the Barbarian's soul, a possibility to solve both the low level and the daily needs problems is to "time-skip" the adventures needed for the players to obtain the levels needed to survive this lower plane.
Basically, you can ask the players to improve the levels of their characters until a certain point (for example, the 9th level which allows your Paladin to cast create food and water, as KorvinStarmast answer says). Equipment/gold should be improved as well, according to the appropriated for their new levels.
In-game, this could be justified by the characters realizing that Hell is not for beginner adventures as them, and so they spend a time training to improve their abilities and adventuring to get the needed resources (money, magic items, NPC contacts etc) to their hellish journey.
Obviously for many parties this approach can remove the fun of the process of leveling your characters gradually, through "on-screen" adventures, but it has two advantages: firstly, it helps your players to achieve their goal now (in RL time, instead of weeks or even months of adventures); and secondly, specially if your players never played a high-level adventure, they can experience how is to have powerful characters (note that this can be a problem for the GM, since it's usually harder to manage higher than lower level PCs).
Another possibility to both problems: give them some artifacts or powerful magic items to compensate their lower level AND help to satisfy their daily needs, which only works during this specific quest.
The ingame reasoning for that can be the following: the Barbarian sacrificed his soul to save his friend, a paladin of Bahamut, a Lawful Good god. According to that Forgotten Realms wikia,
Bahamut was stern and very disapproving of evil, always arguing with Asgorath about his crusade against it. He accepted no excuses for evil acts, and didn't tolerate even minor offenses by evil creatures.
In spite of his stance, he was also considered one of the most compassionate beings in the multiverse. He had limitless empathy for the downtrodden, the dispossessed, and the helpless.
So, Bahamut would not want to see a devil obtaining another soul to "play", after all he could not tolerate a victory for Evil. And, while he would censor the Barbarian deal with a devil, he could be empathetic toward his sacrifice for a comrade. Consequently, Bahamut offers, maybe toward their clerics of even by his avatar, some powerful items, but these will be removed from them after the journey ends, and can only be used in this quest (so the players can't cheat by receiving the items and engaging in unrelated adventures to get XP and treasure).
Two possible problems of this approach: firstly, it could be hard to balance or manage these artifacts, and secondly, the players can become very attached to the powers of such powerful items, and so they can resent the moment Bahamut recall them.
(as a bonus note: I remember to have read in an old RPG magazine that the Dungeons and Dragons cartoon characters are very low level, coming from RL non-fantasy Earth, but they compensate that by their powerful magic items).