Stripes solution
by Kegler

The state abbreviations for the original 13 colonies (representing the stripes on the flag) are added to the theme answers.

Stripes solution grid

Across
1OT + HER (TO rev)
4ANIMALS (SNAIL anag)
9B(R)IGADES
11UNlIT
12VIVAC + IOUS
15A + LDA (LAD anag)
16WON ("ONE" hom)
17ANTE (NATE anag)
19BE(D + L)AM
21GON(D)OLA (LAGOON anag)
22EYED ("I'D" hom)
23prELUDE
24CON(SIS)T
26C + ON + CH
29CAPAB + LE
32ACE (hidden)
33GARDENER (2 defs)
35ST(R)EAMS
36RAJ + AS (rev)
37DO(P)E + Y
38TANH (1st letters)
Down
1OB + VI + ATED (BO rev; DATE anag)
2TRI + ANGLE
3EGAD (AGED anag)
4AD + I-T
5NEwtON
6MUSC + LES
7A + WNYAY (YAW rev)
8STONE + D (NOTES anag)
10SUNDANCE (AND USE anag)
13CAMD(E)N
14COMES CLEAN (SOME CANCEL anag)
18ENDE(A + RE)D
20E + LOPERS
24C-CL + AMP
25OPERA (A ROPE anag)
27NINJA (even letters)
28HA(R)SH
29C + ASH
30ACT'S
31B(E)AT
34DoRY