Larry gave you great advice.
Gunpowder Hatch Chart:
Big Gunpowder Falls River, Maryland Hatch Chart - Fly Fishing Community
Savage Hatch Chart:
Savage River, Maryland Hatch Chart - Fly Fishing Community
Based on the hatch charts you could pick up flies specific to your hatches, and pick some up for weeks and streams you plan to fish--- you don't have to buy a ton all at once, but these should be good patterns if you wanted to zero in on a few.
Hendrickson_ - Dries Hendrickson (for female) and Red Quill (for male) size 14 would be good choices if you order on-line, but you may want local patterns from a fly shop--- this can be a tough hatch
March Brown – dries March Brown 12 (Nymph March brown nymph size 12 or could use Bead Head Gold Ribbed Hares Ear size 14)
Caddis – tan and olive fluttering caddis in size 14, Emerger olive sparkle caddis or z wing 14, Emergent Sparkle Pupa (Olive) 14
Light Cahill Dries: Light Cahill or Cahill Sparkle Dun 14. Light Cahill Nymph 14 (or Gold ribbed Hares Ear comes pretty close though a bit darker)
Sulfur Dries: Sulfur Sparkle dun, Parachute Sulfur, and PMD or Sulfur Spinner 16 and 18, Sulfur Emerger 18, Nymph Pheasant Tail Sulfur ( or can use Pheasant Tail Nymph) 16 and 18 Sparkle duns tend to fish better for this hatch than hackled patterns, and the emerger can be important
Pale Evening Dun: Parachute or Sparkle Dun PMD 16,18 or use sulfur patterns
Gray Fox: Gray Fox or Tan Sparkle Dun 14, Nymph Bead Head Gold Ribbed Hares Ear 14
Eastern Green Drake: Eastern Green Drake or Gray Fox Variant (for dun) and Coffin Fly (for spinner) 10, 12, Eastern Green Drake Nymph 10 This is a hit or miss thing, but if you catch it right it can be great fishing, The spinners hit the water around dusk, and can be very important. The duns and spinners are good flies to have for a lot of waters in the East. And fishing these even when no hatch is going on during the time they "should" be hatching often brings strikes on waters where they occur.
Brown Stone Kaufmann’s Stone (brown nymph pattern) size 12
In addition to being good for specific hatches, these flies make great good searching patterns. To these specific "hatches matchers" you could add some generic flies like black buggers size 8, muddler minnows size 10 (will double for both sculpin minnows and grasshoppers) etc. to cover a few more bases.
All of these above flies, plus others not mentioned on the above hatch charts like Blue Wing Olives 16-22 all season, Blue Quills 18-20 early spring, Quill Gordons 12-14 early spring (probably over now), Isonychia 10-12 (spring) and 12-14 (fall), Tricos 18-24 (August), White Flies 10-12 August (Use cahills or white Wulff) mayflies and the Yellow Sally stonefly (a yellow stimulator size 12 works well in late spring early summer) are pretty common in the East on many streams, with hatches occurring a few weeks later than your streams as you move North, and are on many of your streams as well, at least sporadically.