I couldn't think of an expression that fully covers both parts of útravaló. I thought of ways to describe something that you might give to someone, and ways to express the ideas of useful and helpful items, especially in times of trouble. Getting both concepts into the same expression was a bit of a challenge, however.
One candidate I considered was goody bag. This term refers to a bag of items – usually promotional items, such as samples or coupons – that are given away at check-in time, to conference registrants, road race participants, golfers participating in tournaments, etc. Wordnik list this among its definitions:
A bag containing gifts and promotional material handed out at a conference, exhibition or similar event.
That almost has the right connotation. After all, goody bags often contain something useful for the event. A golfer's goody bag might have golf tees; a conference goody bag might have a pen and a blank notebook; a marathoner's goody bag might contain an energy bar or sample of chafe cream. That said, the contents of a goody bag are usually rather inessential, and not likely to come in handy during a trying ordeal or time of danger.
One other term that crossed my mind was survival kit. Survival kits contain some basic items that are likely to be extremely useful during a time of emergency. Wikipedia says:
A survival kit is a package of basic tools and supplies prepared in advance as an aid to survival in an emergency.
Survival kits .. contain supplies and tools to provide a person with basic shelter against the elements, help them keep warm, meet their health and first aid needs, provide food and water, signal to rescuers, and assist them in finding their way back to help. Supplies in a survival kit normally contain a knife (often a Swiss army knife or a multi-tool), matches, tinder, first aid kit, bandana, fish hooks, sewing kit, and a flashlight.
It seems the contents of a survival kit are more in line with útravaló than the contents of a goody bag, but survival kits aren't typically given from one person to another, unless they are issued by an employer or agency. Instead, they are likely to be found as standard equipment in places like ships, outposts, or military aircraft.
Your comment about magical objects given to folk tale characters prompted me to look over various literary devices, such as Deus Ex Machina, to see if there might be something akin to útravaló. During that search, I found Chekov's Gun, which seems close. One website defines Chekov's Gun as:
A literary technique whereby an unimportant element introduced early in the story becomes significant later on. For example, a character may find a mysterious necklace that turns out to be the power source to the Doomsday Device, but at the time of finding the object it does not seem important.
Chekov's guns are often stumbled upon, not given; however, the more I studied examples of Chekov's guns, the more I thought the term aptly described Lucy's vial of healing elixir (from The Lion, the Witch, and the Wardrobe), which had been an earlier gift from Aslan – and, if I understand the concept correctly, that vial could indeed be described as an útravaló of sorts.
In short, Chekov's gun is no perfect match for útravaló, either, but there can be a bit of overlap, depending on how the device is wielded in the story. I also think something like words of advice, heeded later on, can be a type of Chekov's gun.