Selecting a transistor for high-side switching at 5V with a 2A load current
You want a P channel MOSFET.  You need one that has nicely low Rdson with only 5 V gate drive, but that shouldn't be too hard since your voltage requirements are low.  You can probably find one in the small 10s of m&Omega; range.

For example, let's say you find one with 35 m&Omega; at 5 V gate drive.  At 2 A, that will drop only 75 mV, so your output will be 4.925 V.  The power dissipation is (2 A)&sup2;(35 m&Omega;) = 140 mW.  That's probably borderline for a SOT-23 package - check the datasheet.  It sounds appropriate for a SOT-89 package, but as always, check the datasheet.

Another option is to parallel two MOSFETs.  That cuts the total dissipation by 2, and the dissipation of each by 4 relative to a single FET.  Two of the same FET's in parallel from the above example would only dissipate 70 mW total.  Ideally each will dissipate 35 mW, which you'd barely notice getting warm.  They won't share the current exactly equally, but even if one dissipated all 70 mW, a SOT-23 would still be fine.