Here's an idea for a resource you can't bring a pile of in a backpack. First, make the assumption that ICE, or whatever you choose to call it, talk to each other. This is what actually happens in real life, of course. Security software gathers information on attacks and sends it back to the vendor, which updates its defenses for the new attack. Assume this process is automated with AI. Then any particular piece of breach software becomes less useful each time it's detected, as the defenses improve. So a hacker will probably carry several types of attack software, each with particular strengths and weaknesses. He has to write these himself or buy them custom-made, because each time one is used it becomes less useful, so anything found in a public resource is likely fully compromised. It takes a significant amount of time, research, experimentation, and money to write these.
So for the game mechanics - the hacker writes his attack software and it uses up significant amounts of an important resource, like money, time, or xp. Every time an attack is made with that software, it gets a -1 permanent penalty to future uses, with an additional -1 if the attack fails, as the collective defenses of the world have learned just a bit more about it. Eventually it's useless and the hacker will need to write some more.