This is potentially a huge topic with a lot of room for work, but I'll start small by picking what seems to be some of the low hanging fruit.
Mortal Stunts
Call in the Cavalry: You are a member of a major organization, or have close ties to one. Because of that connection, you can rely on them to back you up when the shit really hits the fan. Once per adventure, you may call upon that group to aid you directly. That aid takes the form of one individual or several who will assist you and protect you, even to the extent of risking their lives, so long as your actions match the goals and methods of the organization to which they belong. The GM has the final say in just what form this aid will take, but it typically consists of an individual or group of individuals who would constitute "Equal Opposition" (YS 333) to your character. In most circumstances they will aid your character for one encounter before their other duties call them away or their resources are spent. In some situations the organization will be unwilling or unable to extend their aid to the PC in question; treat this as a compel against one of the character's aspects or an aspect related to the current adventure.
Trusty Ally: With this stunt you are accompanied through life's travails by a devoted ally. The relationship between the two of you might be personal, professional, mystical, or anything else, but come hell or high water, you are in it together. Choose a high concept and two aspects for your ally. Your ally has no refresh to spend on powers and stunts, but may choose one skill at the level of one below your skill cap (So if your skill cap is Great, they may choose one to have at Good). They also choose two skills at the level below that, three skills at the next level down and so on. This ally tends to be useful in one or a small group of related situations, but not in others. For example a secretary ally would be good at doing research and deflecting unwanted social attention, but would be of less use in a fight. Keep this in mind when designing your ally's skills and aspects.
Band of Brothers: Requires Trusty Ally. If two minds are better than one, why not take that to its logical conclusion? You have a knack for attracting like-minded individuals to your cause, whatever that may be. You could be the captain of your department's Special Investigations, you could be a Cult Leader, the point is that you know how to lead. The first time you purchase this stunt you may have up to three allies, constructed according to the guidelines given in the Trusty Ally stunt. If you buy this stunt again you may have a large group of such allies, easily up to a dozen.
Partner: Requires Trusty Ally. You're not interested in a sidekick so much as a partner, someone who can keep up with you when the going gets really rough. The ally you gained with the Trusty Ally stunt is granted 3 refresh to spend on stunts and powers, as appropriate to their High Concept, and 5 skill points. You may purchase this stunt again, each time granting your ally 1 more refresh and 2 skill points. The added skill points give this NPC more scope to interact with the campaign, making them useful in a broader array of situations than an unimproved ally. Your GM has the final say in determining how powerful you can make a partner before it eclipses the importance of your actual character.
I've tried to incorporate a few different ideas into getting started on the mortal end of this problem, though these stunts could also be used to make familiars and other things. One thing that is very important is that not every NPC that is important to your character has to be modeled using these rules, in fact the VAST majority of the time you should skip it and just throw in an aspect on your sheet that mentions them. These abilities are specifically for NPCs that you want to be able to control in-game, and thus that you foresee playing an important role in almost every adventure you participate in.
